Sword of Spirit
Legend
There is an impression out there that the monster creation rules in the 2014 DMG don’t work.
I disagree. I haven’t had any problem making monsters with them, and there are others that can say the same thing. I’ll try to keep my rambling thoughts and theories in the footnotes(1) and focus on the practical process.
Some say the rules don’t work. I say they do(2). I intend to try to prove it.
I’m going to make about 5 monsters(3), with little or no pre-planning. I’m just going to think up a monster idea, open up the DMG and MM, and make it happen. And I’m going to tell you what I’m doing and how it relates to the DMG rules every step of the way.
Let's start with the idea that came to me as soon as I had the idea to write this up this morning: the Thwumper.
If you are planning to create a monster, we can assume you already have sufficient creativity, or you are working on developing it. At this step you just come up with the general concept of your monster in sufficient detail to feel like you can start D&D-ifying it.
The thwumper will be a giant, dome-shaped, many legged, beetle sort of thing(5). I want to give it a special ability that allows it to create a little earthquake thing centered right beneath it, its “thwump” ability.
Step B(6) Come up with an expected CR. Resources Needed: Monster Manual, experience.
For this step, you need to have an idea of what sorts of monsters the various CRs represent. Your best and simplest resource here is a Monsters by CR list. Here’s a link to the official one from WotC.
Decide about how tough you want the monster to be, using that list as a guideline. You either need to have enough experience to know how tough monsters on the list are, or you can just look them up and read their entries in the MM. Once you find the right challenge, you know your expected CR(7).
For the thwumper, I want it to be a pretty scary challenge for low level characters they might rather avoid, but something mid-level characters won’t have too much of a problem with. At this point, I’m also clarifying for myself its size, so I can better visualize it relative to the other monsters. It’s not quite as big as the Huge bull African elephant (itself probably one of the smallest Huge creatures in dimensions, if not mass), but it's pretty big, so Large is the right size.
CR 5 sounds like a good starting point as a scary challenge for low level characters, so I’ll look in that general area on the list. Right off the bat I see a Bulette. That immediately sounds pretty close to what I’m going for. As I look down the list, I also see Hill Giants (feels like about the right power level). So CR 5 is looking pretty good to start.
But I want to be sure so I’m going to look at CR 4 and CR 6. CR 4 has that Elephant, and while this creature is smaller than an elephant, it’s a monster that I see as being tougher. CR 6 is a Mammoth(8), and right in the middle seems like a great fit.
CR 5 it is.
Step C Decide on the stats you know you want. Resources Needed: Monster Manual, Player’s Handbook, experience.
At this point, you may already know what you want certain things in the stat block to be. Look at a monster stat block, and go down the line jotting down stuff you already know you want from the following list: name, size, type, alignment, ability scores, AC (ballpark only), hit points (ballpark only), resistances, immunities, vulnerabilities, equipment, traits, special actions and reactions, speed and movement types, save and skill proficiencies, senses, and languages(9).
Do not do any math at this point. Do not try to figure out how much damage an attack does. Only jot down things you already know you want. And it’s fine to just use estimates.
I already know its name, and that it’s going to be Large. Monstrosity is the best fit for its creature type, as it’s not intended to be weird enough to be an aberration. It’s an unaligned creature.
The Bulette’s AC is 17, but I don’t have a problem going a bit higher than that, and 18 is calling to me, so its AC is tentatively 18 from natural armor.
It should have plenty of hit points, but I don’t see it as having particularly more or less than you would think by looking at it. I look at some other monsters of similar size, shape, and CR, with a particular emphasis on monstrosities. Bulette CR 5, 94 hp; Gorgon, CR 5, 114 hp; Umber Hulk and Young Remorhaz, both CR 5, both 93 hp. And for extra data, Elephant, CR 4, 76 hp; Mammoth, CR 6, 126 hp. I could keep going, but a pretty good pattern is emerging here. About 93/94 is coming up multiple times, and the ones that are higher are supposed to be super tanks (which the Thwumper isn’t), so we have a pattern. I’ll just tentatively jot down 94 hit points, but it could easily go from 85 to 105.
While I was looking at those monsters I also noted AC for Bulette, 17, Gorgon, 19, and Umber Hulk, 18. Knowing what those monsters are, that convinces me. 18 is the right AC.
Nothing stands out for resistances or immunities, though we might spruce it up with something that won’t affect the CR later(11). No vulnerabilities(12). Obviously no equipment.
For special traits, nothing immediately comes to mind, but there’s a good chance I’ll think up something later.
For special actions, we will have the thwump! They can use some sort of sonic effect to cause an earth tremor underneath them that can knock down nearby creatures. Maybe it will do some damage too, maybe it won’t. We’ll wait and see. I’m thinking that if it does damage it will be an action, and if it just knocks them down it will be a bonus action. In any case, it will be on a recharge for usage. We don’t want any math here yet, though if we had a monster that already had a similar attack and we wanted it to be almost exactly the same, we could jot down a ballpark damage figure. No reactions come to mind.
For speed and movement, I don’t imagine it as being particular fast. In fact, I kind of imagine it as being slower than normal, but that might not be a good idea, because it means characters can just walk backwards and kite it until it’s dead, making it much weaker than it should be. We’ll worry about that later, just noting the potential issues. Should it have a burrow speed too? Probably!
While I was thinking about the speed, I thought of a similar critter from Fell Seal that has this charge that lets it move any distance. Charging any distance doesn’t make sense here, but having some sort of charge attack (maybe rolling into a ball to do it?) sounds cool, and I put it down as a potential option.
I don’t have many thoughts on save proficiencies at the moment so nothing to write down. For skills, maybe Perception, but we’ll think about that later(13). For senses, tremorsense sounds good. Maybe we’ll make it blind and give it blindsight too, maybe not. It’s an unintelligent, unaligned creature; it doesn’t speak any languages.
I noticed that I forgot to jot down any ability scores. That’s actually fortuitous, because during the AC and hp steps I looked up some reference point monsters, so I can look at their stats for ideas. Bulette: Str 19, Dex 11, Con 23, Int 2, Wis 10, Cha 5. Gorgon: Str 20, Dex 11, Con 18, Int 2, Wis 12, Cha 7. Umber Hulk: Str 20, Dex 13, Con 16, Int 9, Wis 10, Cha 10. Young Remorhaz: Str 18, Dex 13, Con 17, Int 3, Wis 10, Cha 4. For the beasts, Elephant: Str 22, Dex 9, Con 17, Int 3, Wis 11, Cha 6. Mammoth: Str 24, Dex 9, Con 21, Int 3, Wis 11, Cha 6.
For Strength, I don’t see it having the ability to exert a lot of musculature in its attacks, so it should be average or a bit below average for its size, shape, and CR. But I also know I don’t want to go too low because it will be using this for its attacks (I don’t want its thwump to be its standard round by round attack). I’m going to tentatively place it at 18, the same as the lowest one on the list, the Young Remorhaz. Might change it later.
For Dexterity, it’s looking like we want something between 9 and 13. It’s also possible we could go even lower. So I’m just going to jot down “not high” for this, because I know that much.
For Constitution, it should be at least average, but it doesn’t need to be super high. It should probably be at least 17, but I don’t have a firm upper limit on it. That’s good, because we can tweak it to the best place to get our derived stats later. I’m going to jot down 17-22.
For Intelligence, I definitely don’t want it above 2. But it is insect-like, and I know they often have an Int of 1. Since I have a spreadsheet of some monster stats(14), I check out which ones have an Int of 1. I still have my size Large filter on, and I see that Ankheg and Carrion Crawler are both monstrosities with an Int of 1. Yeah, that’s it, Intelligence 1.
For Wisdom, an important thing to remember is that it effects the ever important Perception—though you can counteract a low Wisdom with proficiency or double proficiency (“Expertise”) in Perception if you want to. Nothing really stands out to me about this creature’s perceptive abilities, so I’m going to leave it at the average of 10 or 11.
Charisma can be a bit tricky, because oftentimes creatures that are more magical or supernaturally scary and such might have good Charisma, as well as any creatures who base special abilities off it. The Thwumper doesn’t have to worry about any of that, so I’m going to look up Carrion Crawler and Ankheg, for the bug similarity, which gives me 6 and 5. (I also note that they have Wisdom scores of 13 and 12, so maybe I should go higher there.) Looking at the Charisma of the other creatures, I feel like a 6 is probably appropriate here as a guess. It’s not really going to matter for this creature, so I can adjust it later for pure statblock aesthetics if I want to.
I also didn’t think of what its Burrow speed should be, so I just looked up the burrow speeds of other creatures. Those who are supposed to be ridiculously good at burrowing have it equal to their walk speed, those who are pretty good have it a bit less, and those that are more natural creatures (like badgers) have it at a pretty low number. I see the Thwumper as being in the middle, so it should probably be a bit slower than its walk speed—unless its walk speed is lower than 30, in which case burrow should probably be equal so it stays meaningful. So that pretty much means it should be 20, as its walk speed isn’t going to go below that.
So before we even mess with the math, we know the following with a pretty high degree of certainty(15):
Thwumper
Large monstrosity, unaligned.
AC 18 (natural armor)
HP 86-100(10)
Speed 20 or 30, Burrow 20
Str 18
Dex not high
Con 17-22
Int 1
Wis 10
Cha 6
Special Action or Bonus Action 1: Thwump. The creature emits a sonic burst that causes a tremor in the ground below it. All creatures other than the thwumper within X feet must make an X save or be knocked prone, and maybe take XdX bludgeoning damage.
Special Action 2: Some sort of charge. The thwumper moves up to X feet directly towards a target and makes an attack (or forces a save) dealing XdX bludgeoning damage on a success.
That’s a pretty darn good start and we haven’t had to do any math yet(16)! Which brings us to…
Step D Determine the math so far. Resources Needed: Monster Statistics by Challenge Rating table, DMG Step 4 of “Creating Quick Monster Stats”, DMG Steps 9 – 15 of “Creating a Monster Statblock”, Monster Features table.
Now we determine what the things we already know we want the monster to have tell us about the math so far. It’s really straightforward once you understand how it works, but it will be easiest to explain by using our example.
For the Defensive CR, we know that the Thwumper’s hit points will be between 86-100, which puts them on the CR 2 line of the table. We now adjust that CR based on their AC. Their AC is 18, which is 5 points higher than the AC 13 that the table associates with CR 2. Every two points by which the AC exceeds the hit point line increase the Defensive CR by 1. Since we have increased it by 2 twice, we increase the CR by 2.
The Defensive CR can also be influenced by five other factors:
1) If the monster has 3 or more damage resistances and immunities(11)
2) If they have any spells that can affect their AC(17)
3) If the monster can make ranged attacks while flying
4) If the monster has 3 or more saving throw proficiencies
5) Special traits, such as those on the Monster Features table(18)
None of those apply to the Thwumper at this point. We already know 1-4 will not be used, and since we haven’t chosen (or created) any defensive special traits, we can jot down their current Defensive CR as 4. If we make any defensive traits, they could raise it.
We don’t have enough information at this point to come up with an Offensive CR so far. Much of the time you won’t at this point. The main exception is if you are using an equipment-based creature and you know its attack stat. Then you could combine the weapon’s damage, with the attack stat from the damage, how many attacks it gets a round, the proficiency bonus from its expected offensive CR, and use the table to determine what the actual current Offensive CR is(19).
What we can do is note the math that will help us determine it later.
With Strength-based attacks, our Strength score of 18 and the proficiency bonus of +3 from a CR 5 creature tells us that its attack bonus will be +7. We also know that we will be adding +4 to the damage from the dice value we use for its attacks.
For the save DC on its thwump ability, Constitution is the best stat to use. We imagine this sonic thwump thing coming from its monstrous anatomy not its mind--which is good because its mental stats are not combat worthy(20). It will probably be equal or higher than Strength, so it has the benefit of also using it’s highest value. We want this to be a good special attack!
Its Constitution is going to be 17 to 22. Using the save DC formula (8 + proficiency bonus + ability score modifier) we know the save DC against its thwump is going to be 14 to 17.
The ability to knock creatures down has no effect on the CR normally. However, if we make it a bonus action and let them use it before it makes its attack(s) for the round it could grant it advantage on its attacks for the round, which would increase its effective attack bonus by 4 for that round(21). We still haven’t decided whether its going to be a bonus action that doesn’t cause damage, or a standard action that does, though I’m leaning towards the latter.
For its charge ability, it will be Strength-based, so it will either have an attack bonus of +7, or a Save DC of 15.
So what can we tell regarding the Offensive CR at this point? Well, since the Defensive CR is 4, that means we need an Offensive CR of at least 5 to hit the overall CR of 5 we want. Unless its saving throw abilities end up be more contributive to its damage output than its attack, we can now use the table to determine what range its per round damage should fall within it. The attack bonus for the CR 4 damage line is +5, so if we used the CR 4 damage, our +7 would be 2 higher and raise it to a CR 5. Or we could just use the CR 5 damage line, which has an attack bonus of +6, so our +7 wouldn’t raise it. That means the damage output per round should be 27-38.
And that’s about all we can or should determine about the math so far.
Step E Experiment with attacks, traits, and special abilities. Resources Needed: All of the above.
This step could be long or short, depending on how complex your creature is and how much you already figured out about their stats in Step C. Essentially, we want to see if there are any traits or features we might want to give them that haven’t occurred to us yet, create possible stats for their damage, as well as any other actions, bonus actions or reactions.
Whenever you pick or choose potential features (such as from the Monster Features table) that have an effect on CR, you want to make a note of what that effect does, such as “Fiendish Blessing: Cha mod to AC”. Don’t apply those effects yet, just determine what they will do if you do apply them.
By the end of this step, we should have all the components we need to finalize the creature’s CR relevant stats in the next step.
For the Thwumper, we know we still need a few things. For the first, I want to see if there are any special defensive features I might want to give it. Brainstorming, I would kind of like the ability for them to withdraw into their shell and increase their defenses. Maybe they even can (or must) do it at the same time they activate the thwump ability.
Off the top of my head, I can think of two creatures that can do that, the Flail Snail, and the Tortle(22). I’ll use them for the template for this ability. I’m not sure if it needs to grant the full +4 AC, since this creature is mostly in its shell all the time, so I can drop it to 3 or 2 in the future if that would help with the math.
Shell Defense (Action): While standing on solid ground(23), the thwumper withdraws into its shell. Until it emerges it gains a +4 to AC and has advantage on Strength and Constitution saving throws. While in its shell its speed is 0 and can’t increase, it has disadvantage on Dexterity saving throws, it can’t take reactions, and the only action it can take is a bonus action to emerge.
This feature will do absolutely nothing to the creature’s CR, since it isn’t doing anything offensive on turns it spent its action to hide in its shell. Using this feature is an ineffective action choice that would actually reduce the monster’s challenge the vast amount of the time. But it’s there because it makes sense and seems cool(24).
Looking through the Monster Features table for possibilities and inspiration, I don’t see anything else there on the defensive front that makes sense. However I do note the Tunneler trait from the Umber Hulk that I like. It doesn’t effect the CR either. Let’s put it in.
On to the Thwumper’s offensive features. We could do this in any order. I’m going to start with their standard round by round attack.
We’re aiming for a damage output of 27-38, and we need to include a +4 from Strength to each attack as part of that. I’m planning on splitting that between two or three attacks.(25)
To start, I’m going to look at physically similar attacks from other large creatures. An Ankheg’s bite does 2d6 + mod damage. An Umber Hulk’s mandibles do 2d8 + mod, and its claws do 1d8 + mod each. Three attacks along those lines will get me into the right damage range, so sounds good! I don’t want to give it any pincers, but maybe some slashing claw legs to go with its mandibles. Let’s try putting that together as:
Multiattack. The thwumper makes three attacks: two with its slashing legs and one with its mandibles.
Slashing Leg. +7 to hit, reach 5 ft, 1d8 + 4 slashing damage.
Mandibles. +7 to hit, reach 5 ft, 2d6 +4 slashing damage.
That gives us 28 damage, putting us on the CR 4 damage line, which goes up to CR 5 with our attack bonus.
Offensive CR takes the average damage from three rounds. They will bite on two of their rounds, and do their thwump on the other one. Note that since we are on the lower side of our damage, we can feel free to make that thwump more dangerous. The maximum damage we can do with the thwump without raising the Offensive CR for that round above 6 (which would still leave them at an overall CR of 5) is 22. Since it’s an area of effect attack, we assume it hits two characters for a total damage of 44, with a maximum save DC of 16. Note that we most certainly are allowed to raise the Offensive CR above 6, since the damage is for a single round and will be averaged with the damage of the other rounds. I just wanted to demonstrate how the math and the table were intersecting.
Off the top of my head I can’t think of any creatures that do this effect. The earth tremor spell is the closest similar effect. Although spells love to do d6s for damage, I want to make the damage more random on this, so I’m going to use bigger dice.
Thwump. The thwumper sends shock waves into the ground in a 5 foot radius. Each creature on or under the ground other than the thwumper in that radius must make a DC (15 or 16) Strength saving throw or take 4d8 bludgeoning damage(26) and be knocked prone. Creatures that succeed on their saving throw take half as much damage and are not knocked prone.
Note that I made some conceptual decisions as I wrote that up. I decided I didn’t want it to turn the earth into difficult terrain. I also wanted to make sure they were taking some damage even if they made their save. And that implies to me that this isn’t purely a normal earthquake. There is some sonic stuff going on there that kind of resonates with the ground and anyone on it. I could split up the damage into bludgeoning and thunder, but I don’t think that’s entirely necessary. It’s still really the ground that’s directly messing with you, but it’s messing with you even if you manage to not fall down. But I made the save Strength instead of Dexterity, because I think that better expresses how this unusual attack is affecting its targets. You could go with Dex or Con instead if you really wanted to.
A brief note on knocking a creature prone. Remember how I said early in the post that if that’s all it did it would be a bonus action? That’s because knocking creatures prone as an attack rider doesn’t affect the CR. This is almost certainly because characters can just stand up at the start of their turn, just losing a bit of movement. But if I could use a bonus action to potentially knock multiple creatures prone, and then attack them, I’d be giving myself advantage, which very well could affect the CR(27). I decided to keep it simpler and just have a damage + prone ability as the thwumper’s action for the turn. In this case the prone status doesn’t affect CR.
I have some other thoughts about what I might do with this attack, but I’m going to work on some other stuff and come back to it.
Moving onto the charge attack, I realize I need to make some conceptual decisions. How agile do I want the Thwumper to be? While the inspirations were pretty slow and unwieldy I can blame some of that on 1980s special effects(5). I could probably keep its speed at a lumbering 20 and come up with innovative ways to make up for it with special abilities, but I don’t think I’m going to go that route. On the other hand, I could make it a very agile creature, probably with a Climb speed, and have it turn into a potentially bouncing bowling ball kind of thing. I’m not really wanting to go that far in that direction either. I’ll probably stick with a walk speed of 30, a burrow of 20, and possibly a climb (also 20). I have a hard time seeing this creature be able to just have massive bursts of running speed, so I think I might go with the curling into a ball charge.
Rolling Charge. The thwumper launches itself forward across the ground in a line 60 feet long and 10 feet wide, rolling into a ball as it does so. Every creature within that area must make a DC 15 Dexterity saving throw or be knocked prone and take 5d10 bludgeoning damage.
In this case I made the save DC Strength-based. I looked up the Rolling Ball trap in the DMG for some thoughts, and noticed they made it a Dex save with no damage on a success, so I went with that. As an area effect we assume it hits two targets. And while it’s not in the monster creation section, the DMG rules on spell damage say that if you take no damage on a successful save the spell’s damage can be 25% higher for the same level. Total damage of this spell against two targets adds up to 55, and dividing that by 1.25 we get 44 for the effective damage I’m going to plug into the chart. That leaves this as another CR 6 offensive ability. So far that’s 2 out of 3 of offensive abilities are CR 6. That’s perfectly fine, because we could do Offensive CR 6 abilities every round and still hit our creature target CR of 5.
Something that has been rolling around in my mind, with the current concept of the thwump ability, is the idea of stunning the targets. That definitely should make the ability more powerful if it actually prevents characters from acting, but if I have it end at the start of each target’s turn, it will really only stop them from taking reactions. While situationally useful, those situations are going to be rare enough in context of this monster’s normal usage that it isn’t going to raise the CR. Since it really adds some more flavor to the thwump, let’s do it. Also, with that change, Strength no longer makes sense as the save, and we are squarely in the Constitution save territory.
I kind of want to give them immunity or resistance to acid. There’s no really good reason for this. Ankheg’s do acid damage and they aren’t even resistant. But something about it sounds interesting. So I’m going to do it and come up with lore justification later. A single resistance or immunity has no CR effect.
Looking up some monsters with tremorsense, the range is typically 60’ feet, so I’ll go with that. I don’t see any compelling reason to give them darkvision, but pretty much all monstrosities have it, including bulettes, ankhegs, etc, so they’ll get 60’ darkvision.
As I’ve gone through the process, I’ve decided that it’s probably fine if walk speed is 20 ft, given the other things they have; and they don’t need a climb speed.
This step is where you would also be making multiple versions of features if you aren’t sure exactly how you want them to work, or you aren’t sure if the math is going to go how you want it. For example, I could have made a higher damage version of their multiattack routine, or a lower damage version of their Rolling Charge, but I think they will work fine the way they’ve already turned out. This one has coalesced pretty well, but I might end up making multiple versions of things at this step on some later monster.
Those are all the bits and part we need for the Thwumper, so let’s put it all together properly.
Step F Assemble all the components for a desired overall CR. Resources Needed: Monster Statistics by Challenge Rating table, DMG Step 4 of “Creating Quick Monster Stats”, your previous notes.
Now we take all those components we created in Step C and Step D, and put together a monster. Where you have multiple options to work with, you select the ones with the math to give you the CR you want(28). This is also where you will finalize ability scores, hit points, and any derived values.
Notice that at this point, you won’t be referencing the DMG other than to look at that table (and to remind yourself about the Defensive and Offensive CR adjustments in DMG Step 4 if you haven’t internalized it yet.)
Let’s go right down the monster statblock for the Thwumper and fill in everything.
Thwumper
Large monstrosity, unaligned.
AC 18 (natural armor)
For hit points, we’ll need to determine their Constitution score and hit dice. Looking at how it affects the saving throw DCs of their special abilities, I think we want either a +4 or +5 modifier. Comparing it with those other monsters I made notes on in Step C, I’m thinking +4 is what I want, so Constitution 18. As a large creature it uses d10s for HD. And since the range we want it 86-100, we just math it a bit to see which numbers of d10+4s end up in that range. Turns out, there’s only one that does, 10d10s, for 95 hp.
For Dexterity, it ended up back in the lumbering category, and I see it as less agile the the Dex 11 Bulette. The Elephant and Mammoth have Dex 9, and it definitely isn’t any more agile. Let’s just put it at Dex 8, statistically identical but conceptually lower.
I remember now that I left Wisdom at 10 and planned to think about it more later. Later is now. Since the Ankheg and Carrion Crawler had Perception proficiency, I want to make sure that isn’t a universal “bug” thing, or a universal bug-monstrosity thing. I do a quick check on various bug-like monsters, and learn that many do and many don’t. I don’t see perception as being a strong point for the Thwumper, so there is no need to give it proficiency, or increase its Wisdom any further.
HP 95 (10d10 + 40)
Speed 20’, burrow 20’
Str 18
Dex 8
Con 18
Int 1
Wis 10
Cha 6
I liked the idea of damage resistance to acid. Heck, let’s make it immunity and figure out an excuse later.
With no special defensive features, our Defensive CR stays at 4.
To determine the Offensive CR, we need to average the total damage output over three rounds. We’ll assume it uses its special attacks on two of the rounds, and its multiattack routine on one, for an average total damage of 36. That puts us at the CR 5 damage line. Since its damage output actually relies more on saving throws than attack rolls (over the course of three rounds at least) we compare its save DC to the table, and they are on the same line, so no adjustments. That puts its offensive CR at 5. Averaging Defensive CR 4 and Offensive CR 5, rounds to an overall CR 5.
Damage Immunities acid
Senses darkvision 60’, tremorsense 60’, passive Perception 10
Languages –
CR 5
Tunneler. The thwumper can burrow through solid rock at half its burrowing speed and leaves a 10’ wide, 10’ high tunnel in its wake.
Actions
Multiattack. The thwumper makes three attacks: two with its slashing legs and one with its mandibles.
Slashing Leg. Melee weapon attack, +7 to hit, reach 5 ft, , one creature, 8 (1d8 + 4) slashing damage.
Mandibles. Melee weapon attack, +7 to hit, reach 5 ft, one creature, 11 (2d6 +4) slashing damage.
Thwump (Recharge 5-6). The thwumper causes shock waves in the ground in a 10 foot radius. Each creature other than thwumpers on or in the ground in that radius must make a DC 15 Constitution saving throw or take 4d8 bludgeoning damage and be knocked prone, and stunned until the start of their next turn. Creatures that succeed on their saving throw take half as much damage and are not knocked prone.
Rolling Charge (Recharge 6). The thwumper launches itself forward across the ground in a line 60 feet long and 10 feet wide, rolling into a ball as it does so. Every creature within that area must make a DC 15 Dexterity saving throw or be knocked prone and take 5d10 bludgeoning damage.
Shell Defense: While standing on solid ground, the thwumper withdraws into its shell. Until it emerges it gains a +4 to AC and has advantage on Strength and Constitution saving throws. While in its shell its speed is 0 and can’t increase, it has disadvantage on Dexterity saving throws, it can’t take reactions, and the only action it can take is a bonus action to emerge.
Notice that I increased the radius of its thwump to 10’. I don’t think that will break anything, and fits better with what I’m going for. I also made the recharge of the Rolling Charge less than that of the Thwump. This is purely a conceptual choice. While I like giving it that charge ability, and think it works really well for it, I don’t want it to overshadow the thwump that is part of the creature’s original conceived identity.
Now, with those all put together, we can compare the Thwumper against some of the other CR 5 monstrosities we referenced, and see how it feels.
Comparing it to the Bulette, the Thwumper has slightly better defenses, and slightly worse offenses. It is also a lot slower than the Bulette. Compared to the Young Remorhaz, the Thwumper has significantly better defenses, and about equivalent offenses, though the Young Remorhaz is even more punishing on characters attacking it in melee which might push it higher in offense. The Umber Hulk has similar values for defense and offense, but with less flexibility in attacks. It also has a powerful disabling ability it can use basically at will. Since the Thwumper had to round up to get its overall CR 5, we can assume its one the weaker side of its CR. The Thwumper clearly fits as a CR 5 monstrosity. Compared to the other CR 5s, it is stronger than the Young Remorhaz, on par with or slightly weaker than the Bulette, and pretty clearly weaker than the Umber Hulk with its Confusing Gaze.
If I wanted it to be stronger for its CR, I could give it 1 or 2 more HD, which would move its Defensive CR to 5, still keeping it in the same overall CR 5. But comparing it to other monsters, it feels more like I envision the creature to keep its hp where they are.
Mathematically, the Thwumper is complete.
Step G Polish until it shines. Resources Needed: The results of Step F, creativity, experience.
Here is where we take all of that, smooth off any rough edges, polish up the language to read like a proper 5e statblock, and put any lore and/or art we want to go with it.
As we’re doing so, we can make last minute tweaks, or even go back into a previous step and change our design if we aren’t liking how it all looks when we put it together. You want to have a good idea of how the monster looks and functions overall by the time you are done.
For our Thwumper, the only statistical rough edge to smooth is that I’m going to bump up its even 18 Con to the statistically identical 19 Con because I like it better there.
You'll also note that I removed any vestiges of sonic-ness to its thwump attack, and just referenced vibrations, which is really what I was going for all along.
As I was reviewing the final write-up, I decided I wanted to increase the damage on the thwump attack a tad. By raising it from 4d8 to 5d8, the Offensive CR goes up to 6, which doesn't change the overall CR of 5.
I also need a less comical name for the creature and its signature attack, and some skeletal lore(29).
(1) Heh. Let’s see how well I do.
(2) I do not mean that they are simple, 100% straightforward, or that there is no learning curve. Nor do I mean that there aren’t a few rough spots (which I will address as they come up), nor that the presentation in the DMG is done well. But they do what they are primarily designed to do: tell you what the CR of this creature you just made should be, and create monsters that perform approximately at that CR, within a reasonable margin of error. I’m also not claiming that I will perfectly explain it. Feel free to bring up any “What about”s or “You’re totally not addressing”s. Chances are I have taken that into account but I didn’t think to mention it.
(3) Assuming I don’t run out of steam and never get back to it, which happens more often than I would like.
(4) I’m using letters rather than numbers here, so I can refer to the numbered DMG steps with less confusion. Also, as will become obvious, I am not doing it in the exact same order as the DMG does it, because I think my way is more efficient. Nonetheless, I’m using the same math and the same rules.
(5) I’m imagining something like the creatures from The Dark Crystal or The Neverending Story 2.
(6) Before we move forward, you should to know something the book doesn’t explicitly say, and I think might trip some people up. While we are using the “Creating a Monster Stat Block” rather than the insufficient “Creating Quick Monster Stats” rules, “Creating a Monster Stat Block” rules actually are expansions of the other, not pure replacements. You need to read the quick rules first, and you will refer back to them repeatedly.
(7) You might end up moving it up or down by 1 as you get into the details, but if it's a monster you are creating from scratch you probably won’t need to. If you are converting a previous edition monster and want to make sure its CR has a certain relation to monsters of previous editions, or it has an attack that has to do a certain amount of damage for consistency with other monsters, this can become more likely.
(8) Since it’s 2 CR higher than the elephant, I assume we should be imaging the biggest, probably historically inaccurate mammoth we can, rather than the real world ones which probably weren’t 2 CR higher than an elephant.
(9) Those are the order the DMG has them, but you might want to make the list in an order that works better for you.
(10) With my experience, I went back and looked at the table and noted that the hp line that fits the best is the CR 2 line, 86-100 hp, so that’s the value I’m jotting down for hp: 86-100. I wouldn’t have to do that at this point, it just might save me a bit of time later.
(11) Here we’re going to address a rough spot in the rules, the Effective Hit Points Based on Resistances and Immunities table. It’s utter crap. Don’t use it as written. It assumes both that parties will have less ability to overcome damage resistances than is a reasonable assumption, and that characters who can’t overcome damage resistances won’t have any useful way to contribute (and grappling, shoving, or the Help action are a bare minimum of contribution available to anyone). I won’t offer my own replacement for that table yet, both because it’s not finished and because I’m sticking with the rules in the DMG. Just know that if you use those rules the monster will be weaker than its CR indicates.
(12) Vulnerabilities are sort of “advanced design” and you can and should almost never use them unless you have a lot of experience.
(13) Personally, I’d probably give something like this Athletics to help resist grapples and shoves, but I’m not telling people how to make monsters with all my tweaks, I’m going by the book, so no skills unless we decide to give it Perception later.
(14) Not necessary, but it sure speeds things up!
(15) There is of course always the possibility something will change later, and since such changes will likely be for the better, I’ll call that the “happy possibility”.
(16) You’ll notice that even though I said “ballpark only” for some of the things we were figuring out on this step, I actually ended up pretty firm on some things. Once you have a little experience using the system, you learn what things you can and can’t set more firmly at this point. In this creature’s case, it was the AC. It wouldn’t be the same for everything.
(17) This is another rough spot, because they don’t actually tell you how spells affect their defensive CR. If such a spell changes their AC for the duration of the fight, it’s pretty straight forward. For spells that do something else, you need to refer to the Monster Features table to get an idea of what sorts of features adjust the defensive CR in certain ways. For example, the Parry ability which allows a monster to increase their AC against one attack as a reaction increases their effective AC by 1, and the Superior Invisibility Trait, which will impose disadvantage on most attacks against them increases their effective AC by 2. It would be great if there were a table listing specific manipulations like that and how they effect the math, but unfortunately they didn’t give us that.
(18) If you make up your own special traits, you will need to use your own experience and judgment to determine its effect, see note 17. I’m not going to argue with you if you complain about this rough spot.
(19) Another exception is if you are converting a monster or for some other reason already know how much damage it is going to deal, and the ability scores that would affect the attacks or saving throws.
(20) You need to keep that in mind for saving throw DCs. It’s important (at least for me) that the stat used makes sense—you don’t just pick the highest stat because it gives the biggest number. At the same time, you have to fluff it in such a way that you aren’t using an ineffective stat for it, unless it is intended to be something that rarely works in combat that you just turned into an ability for completeness or flavor (which I approve).
(21) See Nimble Escape. This trait is one of the rough spots. It only works as intended for “Forest Archer Goblins”, who can use it to hide behind a tree and take a shot each turn, granting them advantage on all their attacks, and the character disadvantage on all attacks against them. It is significantly weaker in most real game situations, where the goblins might be in melee, or might not be able to hide as easily, etc. However, it does tell us what advantage or disadvantage are worth for monster design: +/-4.
(22) Unfortunately, neither of these are in the Monster Manual, which demonstrates that the more money you give WotC, the more likely you are to be able to figure out how to use the materials you’ve already bought. Hmm.
(23) I put this little caveat in because it can burrow and this shouldn’t work while burrowing.
(24) Advice for running the monster in its write-up should probably tell the DM that this feature is highly situational and shouldn’t be used most of the time.
(25) One of the unstated best practices of monster design is that you should avoid making monsters dependent on a single powerful attack. The reason for this is that it is just too easy for a party to negate that single attack with class features meaning that monster did basically nothing that round. It’s better to make sure they somehow get multiple attacks, even if you need to use bonus actions or reactions to do it. This doesn’t apply to low-level mooks like goblins and orcs and such, and other creatures that are intended to be fought en masse.
(26) Special abilities like this don’t typically add an ability modifier to damage.
(27) This is another rough area in the rules. The same principle would apply if the creature could make multiple attacks in a turn with a prone rider, but the rules don’t account for it. In this case, it doesn’t matter because my creature doesn’t have anyway to attack prone creatures before they have a chance to stand back up.
(28) If you aren’t committed to a specific overall CR, you can just pick the options that give you the math you like best, and take whatever CR you end up with. Theoretically there is a problem with the way the Monster Statistics by Challenge Rating table works. The table depends on your final CR by virtue of using your proficiency bonus (derived from your final CR!) but actually creates the CR at the same time. There is a circular reference that could be a problem. However, I’ve found in practice, since proficiency bonus only changes every 4 CR levels, that that has never actually been a problem. It comes up too rarely to be a significant functionality issue.
(29) I actually prefer lots of lore and multiverse integration on my monsters (2e FTW!), but I’m not going to do that here.
I disagree. I haven’t had any problem making monsters with them, and there are others that can say the same thing. I’ll try to keep my rambling thoughts and theories in the footnotes(1) and focus on the practical process.
Some say the rules don’t work. I say they do(2). I intend to try to prove it.

I’m going to make about 5 monsters(3), with little or no pre-planning. I’m just going to think up a monster idea, open up the DMG and MM, and make it happen. And I’m going to tell you what I’m doing and how it relates to the DMG rules every step of the way.
Let's start with the idea that came to me as soon as I had the idea to write this up this morning: the Thwumper.
Monster 1: “The Thumper”
Step A(4) Come up with a concept for your monster. Resources Needed: Creativity.If you are planning to create a monster, we can assume you already have sufficient creativity, or you are working on developing it. At this step you just come up with the general concept of your monster in sufficient detail to feel like you can start D&D-ifying it.
The thwumper will be a giant, dome-shaped, many legged, beetle sort of thing(5). I want to give it a special ability that allows it to create a little earthquake thing centered right beneath it, its “thwump” ability.
Step B(6) Come up with an expected CR. Resources Needed: Monster Manual, experience.
For this step, you need to have an idea of what sorts of monsters the various CRs represent. Your best and simplest resource here is a Monsters by CR list. Here’s a link to the official one from WotC.
Decide about how tough you want the monster to be, using that list as a guideline. You either need to have enough experience to know how tough monsters on the list are, or you can just look them up and read their entries in the MM. Once you find the right challenge, you know your expected CR(7).
For the thwumper, I want it to be a pretty scary challenge for low level characters they might rather avoid, but something mid-level characters won’t have too much of a problem with. At this point, I’m also clarifying for myself its size, so I can better visualize it relative to the other monsters. It’s not quite as big as the Huge bull African elephant (itself probably one of the smallest Huge creatures in dimensions, if not mass), but it's pretty big, so Large is the right size.
CR 5 sounds like a good starting point as a scary challenge for low level characters, so I’ll look in that general area on the list. Right off the bat I see a Bulette. That immediately sounds pretty close to what I’m going for. As I look down the list, I also see Hill Giants (feels like about the right power level). So CR 5 is looking pretty good to start.
But I want to be sure so I’m going to look at CR 4 and CR 6. CR 4 has that Elephant, and while this creature is smaller than an elephant, it’s a monster that I see as being tougher. CR 6 is a Mammoth(8), and right in the middle seems like a great fit.
CR 5 it is.
Step C Decide on the stats you know you want. Resources Needed: Monster Manual, Player’s Handbook, experience.
At this point, you may already know what you want certain things in the stat block to be. Look at a monster stat block, and go down the line jotting down stuff you already know you want from the following list: name, size, type, alignment, ability scores, AC (ballpark only), hit points (ballpark only), resistances, immunities, vulnerabilities, equipment, traits, special actions and reactions, speed and movement types, save and skill proficiencies, senses, and languages(9).
Do not do any math at this point. Do not try to figure out how much damage an attack does. Only jot down things you already know you want. And it’s fine to just use estimates.
I already know its name, and that it’s going to be Large. Monstrosity is the best fit for its creature type, as it’s not intended to be weird enough to be an aberration. It’s an unaligned creature.
The Bulette’s AC is 17, but I don’t have a problem going a bit higher than that, and 18 is calling to me, so its AC is tentatively 18 from natural armor.
It should have plenty of hit points, but I don’t see it as having particularly more or less than you would think by looking at it. I look at some other monsters of similar size, shape, and CR, with a particular emphasis on monstrosities. Bulette CR 5, 94 hp; Gorgon, CR 5, 114 hp; Umber Hulk and Young Remorhaz, both CR 5, both 93 hp. And for extra data, Elephant, CR 4, 76 hp; Mammoth, CR 6, 126 hp. I could keep going, but a pretty good pattern is emerging here. About 93/94 is coming up multiple times, and the ones that are higher are supposed to be super tanks (which the Thwumper isn’t), so we have a pattern. I’ll just tentatively jot down 94 hit points, but it could easily go from 85 to 105.
While I was looking at those monsters I also noted AC for Bulette, 17, Gorgon, 19, and Umber Hulk, 18. Knowing what those monsters are, that convinces me. 18 is the right AC.
Nothing stands out for resistances or immunities, though we might spruce it up with something that won’t affect the CR later(11). No vulnerabilities(12). Obviously no equipment.
For special traits, nothing immediately comes to mind, but there’s a good chance I’ll think up something later.
For special actions, we will have the thwump! They can use some sort of sonic effect to cause an earth tremor underneath them that can knock down nearby creatures. Maybe it will do some damage too, maybe it won’t. We’ll wait and see. I’m thinking that if it does damage it will be an action, and if it just knocks them down it will be a bonus action. In any case, it will be on a recharge for usage. We don’t want any math here yet, though if we had a monster that already had a similar attack and we wanted it to be almost exactly the same, we could jot down a ballpark damage figure. No reactions come to mind.
For speed and movement, I don’t imagine it as being particular fast. In fact, I kind of imagine it as being slower than normal, but that might not be a good idea, because it means characters can just walk backwards and kite it until it’s dead, making it much weaker than it should be. We’ll worry about that later, just noting the potential issues. Should it have a burrow speed too? Probably!
While I was thinking about the speed, I thought of a similar critter from Fell Seal that has this charge that lets it move any distance. Charging any distance doesn’t make sense here, but having some sort of charge attack (maybe rolling into a ball to do it?) sounds cool, and I put it down as a potential option.
I don’t have many thoughts on save proficiencies at the moment so nothing to write down. For skills, maybe Perception, but we’ll think about that later(13). For senses, tremorsense sounds good. Maybe we’ll make it blind and give it blindsight too, maybe not. It’s an unintelligent, unaligned creature; it doesn’t speak any languages.
I noticed that I forgot to jot down any ability scores. That’s actually fortuitous, because during the AC and hp steps I looked up some reference point monsters, so I can look at their stats for ideas. Bulette: Str 19, Dex 11, Con 23, Int 2, Wis 10, Cha 5. Gorgon: Str 20, Dex 11, Con 18, Int 2, Wis 12, Cha 7. Umber Hulk: Str 20, Dex 13, Con 16, Int 9, Wis 10, Cha 10. Young Remorhaz: Str 18, Dex 13, Con 17, Int 3, Wis 10, Cha 4. For the beasts, Elephant: Str 22, Dex 9, Con 17, Int 3, Wis 11, Cha 6. Mammoth: Str 24, Dex 9, Con 21, Int 3, Wis 11, Cha 6.
For Strength, I don’t see it having the ability to exert a lot of musculature in its attacks, so it should be average or a bit below average for its size, shape, and CR. But I also know I don’t want to go too low because it will be using this for its attacks (I don’t want its thwump to be its standard round by round attack). I’m going to tentatively place it at 18, the same as the lowest one on the list, the Young Remorhaz. Might change it later.
For Dexterity, it’s looking like we want something between 9 and 13. It’s also possible we could go even lower. So I’m just going to jot down “not high” for this, because I know that much.
For Constitution, it should be at least average, but it doesn’t need to be super high. It should probably be at least 17, but I don’t have a firm upper limit on it. That’s good, because we can tweak it to the best place to get our derived stats later. I’m going to jot down 17-22.
For Intelligence, I definitely don’t want it above 2. But it is insect-like, and I know they often have an Int of 1. Since I have a spreadsheet of some monster stats(14), I check out which ones have an Int of 1. I still have my size Large filter on, and I see that Ankheg and Carrion Crawler are both monstrosities with an Int of 1. Yeah, that’s it, Intelligence 1.
For Wisdom, an important thing to remember is that it effects the ever important Perception—though you can counteract a low Wisdom with proficiency or double proficiency (“Expertise”) in Perception if you want to. Nothing really stands out to me about this creature’s perceptive abilities, so I’m going to leave it at the average of 10 or 11.
Charisma can be a bit tricky, because oftentimes creatures that are more magical or supernaturally scary and such might have good Charisma, as well as any creatures who base special abilities off it. The Thwumper doesn’t have to worry about any of that, so I’m going to look up Carrion Crawler and Ankheg, for the bug similarity, which gives me 6 and 5. (I also note that they have Wisdom scores of 13 and 12, so maybe I should go higher there.) Looking at the Charisma of the other creatures, I feel like a 6 is probably appropriate here as a guess. It’s not really going to matter for this creature, so I can adjust it later for pure statblock aesthetics if I want to.
I also didn’t think of what its Burrow speed should be, so I just looked up the burrow speeds of other creatures. Those who are supposed to be ridiculously good at burrowing have it equal to their walk speed, those who are pretty good have it a bit less, and those that are more natural creatures (like badgers) have it at a pretty low number. I see the Thwumper as being in the middle, so it should probably be a bit slower than its walk speed—unless its walk speed is lower than 30, in which case burrow should probably be equal so it stays meaningful. So that pretty much means it should be 20, as its walk speed isn’t going to go below that.
So before we even mess with the math, we know the following with a pretty high degree of certainty(15):
Thwumper
Large monstrosity, unaligned.
AC 18 (natural armor)
HP 86-100(10)
Speed 20 or 30, Burrow 20
Str 18
Dex not high
Con 17-22
Int 1
Wis 10
Cha 6
Special Action or Bonus Action 1: Thwump. The creature emits a sonic burst that causes a tremor in the ground below it. All creatures other than the thwumper within X feet must make an X save or be knocked prone, and maybe take XdX bludgeoning damage.
Special Action 2: Some sort of charge. The thwumper moves up to X feet directly towards a target and makes an attack (or forces a save) dealing XdX bludgeoning damage on a success.
That’s a pretty darn good start and we haven’t had to do any math yet(16)! Which brings us to…
Step D Determine the math so far. Resources Needed: Monster Statistics by Challenge Rating table, DMG Step 4 of “Creating Quick Monster Stats”, DMG Steps 9 – 15 of “Creating a Monster Statblock”, Monster Features table.
Now we determine what the things we already know we want the monster to have tell us about the math so far. It’s really straightforward once you understand how it works, but it will be easiest to explain by using our example.
For the Defensive CR, we know that the Thwumper’s hit points will be between 86-100, which puts them on the CR 2 line of the table. We now adjust that CR based on their AC. Their AC is 18, which is 5 points higher than the AC 13 that the table associates with CR 2. Every two points by which the AC exceeds the hit point line increase the Defensive CR by 1. Since we have increased it by 2 twice, we increase the CR by 2.
The Defensive CR can also be influenced by five other factors:
1) If the monster has 3 or more damage resistances and immunities(11)
2) If they have any spells that can affect their AC(17)
3) If the monster can make ranged attacks while flying
4) If the monster has 3 or more saving throw proficiencies
5) Special traits, such as those on the Monster Features table(18)
None of those apply to the Thwumper at this point. We already know 1-4 will not be used, and since we haven’t chosen (or created) any defensive special traits, we can jot down their current Defensive CR as 4. If we make any defensive traits, they could raise it.
We don’t have enough information at this point to come up with an Offensive CR so far. Much of the time you won’t at this point. The main exception is if you are using an equipment-based creature and you know its attack stat. Then you could combine the weapon’s damage, with the attack stat from the damage, how many attacks it gets a round, the proficiency bonus from its expected offensive CR, and use the table to determine what the actual current Offensive CR is(19).
What we can do is note the math that will help us determine it later.
With Strength-based attacks, our Strength score of 18 and the proficiency bonus of +3 from a CR 5 creature tells us that its attack bonus will be +7. We also know that we will be adding +4 to the damage from the dice value we use for its attacks.
For the save DC on its thwump ability, Constitution is the best stat to use. We imagine this sonic thwump thing coming from its monstrous anatomy not its mind--which is good because its mental stats are not combat worthy(20). It will probably be equal or higher than Strength, so it has the benefit of also using it’s highest value. We want this to be a good special attack!
Its Constitution is going to be 17 to 22. Using the save DC formula (8 + proficiency bonus + ability score modifier) we know the save DC against its thwump is going to be 14 to 17.
The ability to knock creatures down has no effect on the CR normally. However, if we make it a bonus action and let them use it before it makes its attack(s) for the round it could grant it advantage on its attacks for the round, which would increase its effective attack bonus by 4 for that round(21). We still haven’t decided whether its going to be a bonus action that doesn’t cause damage, or a standard action that does, though I’m leaning towards the latter.
For its charge ability, it will be Strength-based, so it will either have an attack bonus of +7, or a Save DC of 15.
So what can we tell regarding the Offensive CR at this point? Well, since the Defensive CR is 4, that means we need an Offensive CR of at least 5 to hit the overall CR of 5 we want. Unless its saving throw abilities end up be more contributive to its damage output than its attack, we can now use the table to determine what range its per round damage should fall within it. The attack bonus for the CR 4 damage line is +5, so if we used the CR 4 damage, our +7 would be 2 higher and raise it to a CR 5. Or we could just use the CR 5 damage line, which has an attack bonus of +6, so our +7 wouldn’t raise it. That means the damage output per round should be 27-38.
And that’s about all we can or should determine about the math so far.
Step E Experiment with attacks, traits, and special abilities. Resources Needed: All of the above.
This step could be long or short, depending on how complex your creature is and how much you already figured out about their stats in Step C. Essentially, we want to see if there are any traits or features we might want to give them that haven’t occurred to us yet, create possible stats for their damage, as well as any other actions, bonus actions or reactions.
Whenever you pick or choose potential features (such as from the Monster Features table) that have an effect on CR, you want to make a note of what that effect does, such as “Fiendish Blessing: Cha mod to AC”. Don’t apply those effects yet, just determine what they will do if you do apply them.
By the end of this step, we should have all the components we need to finalize the creature’s CR relevant stats in the next step.
For the Thwumper, we know we still need a few things. For the first, I want to see if there are any special defensive features I might want to give it. Brainstorming, I would kind of like the ability for them to withdraw into their shell and increase their defenses. Maybe they even can (or must) do it at the same time they activate the thwump ability.
Off the top of my head, I can think of two creatures that can do that, the Flail Snail, and the Tortle(22). I’ll use them for the template for this ability. I’m not sure if it needs to grant the full +4 AC, since this creature is mostly in its shell all the time, so I can drop it to 3 or 2 in the future if that would help with the math.
Shell Defense (Action): While standing on solid ground(23), the thwumper withdraws into its shell. Until it emerges it gains a +4 to AC and has advantage on Strength and Constitution saving throws. While in its shell its speed is 0 and can’t increase, it has disadvantage on Dexterity saving throws, it can’t take reactions, and the only action it can take is a bonus action to emerge.
This feature will do absolutely nothing to the creature’s CR, since it isn’t doing anything offensive on turns it spent its action to hide in its shell. Using this feature is an ineffective action choice that would actually reduce the monster’s challenge the vast amount of the time. But it’s there because it makes sense and seems cool(24).
Looking through the Monster Features table for possibilities and inspiration, I don’t see anything else there on the defensive front that makes sense. However I do note the Tunneler trait from the Umber Hulk that I like. It doesn’t effect the CR either. Let’s put it in.
On to the Thwumper’s offensive features. We could do this in any order. I’m going to start with their standard round by round attack.
We’re aiming for a damage output of 27-38, and we need to include a +4 from Strength to each attack as part of that. I’m planning on splitting that between two or three attacks.(25)
To start, I’m going to look at physically similar attacks from other large creatures. An Ankheg’s bite does 2d6 + mod damage. An Umber Hulk’s mandibles do 2d8 + mod, and its claws do 1d8 + mod each. Three attacks along those lines will get me into the right damage range, so sounds good! I don’t want to give it any pincers, but maybe some slashing claw legs to go with its mandibles. Let’s try putting that together as:
Multiattack. The thwumper makes three attacks: two with its slashing legs and one with its mandibles.
Slashing Leg. +7 to hit, reach 5 ft, 1d8 + 4 slashing damage.
Mandibles. +7 to hit, reach 5 ft, 2d6 +4 slashing damage.
That gives us 28 damage, putting us on the CR 4 damage line, which goes up to CR 5 with our attack bonus.
Offensive CR takes the average damage from three rounds. They will bite on two of their rounds, and do their thwump on the other one. Note that since we are on the lower side of our damage, we can feel free to make that thwump more dangerous. The maximum damage we can do with the thwump without raising the Offensive CR for that round above 6 (which would still leave them at an overall CR of 5) is 22. Since it’s an area of effect attack, we assume it hits two characters for a total damage of 44, with a maximum save DC of 16. Note that we most certainly are allowed to raise the Offensive CR above 6, since the damage is for a single round and will be averaged with the damage of the other rounds. I just wanted to demonstrate how the math and the table were intersecting.
Off the top of my head I can’t think of any creatures that do this effect. The earth tremor spell is the closest similar effect. Although spells love to do d6s for damage, I want to make the damage more random on this, so I’m going to use bigger dice.
Thwump. The thwumper sends shock waves into the ground in a 5 foot radius. Each creature on or under the ground other than the thwumper in that radius must make a DC (15 or 16) Strength saving throw or take 4d8 bludgeoning damage(26) and be knocked prone. Creatures that succeed on their saving throw take half as much damage and are not knocked prone.
Note that I made some conceptual decisions as I wrote that up. I decided I didn’t want it to turn the earth into difficult terrain. I also wanted to make sure they were taking some damage even if they made their save. And that implies to me that this isn’t purely a normal earthquake. There is some sonic stuff going on there that kind of resonates with the ground and anyone on it. I could split up the damage into bludgeoning and thunder, but I don’t think that’s entirely necessary. It’s still really the ground that’s directly messing with you, but it’s messing with you even if you manage to not fall down. But I made the save Strength instead of Dexterity, because I think that better expresses how this unusual attack is affecting its targets. You could go with Dex or Con instead if you really wanted to.
A brief note on knocking a creature prone. Remember how I said early in the post that if that’s all it did it would be a bonus action? That’s because knocking creatures prone as an attack rider doesn’t affect the CR. This is almost certainly because characters can just stand up at the start of their turn, just losing a bit of movement. But if I could use a bonus action to potentially knock multiple creatures prone, and then attack them, I’d be giving myself advantage, which very well could affect the CR(27). I decided to keep it simpler and just have a damage + prone ability as the thwumper’s action for the turn. In this case the prone status doesn’t affect CR.
I have some other thoughts about what I might do with this attack, but I’m going to work on some other stuff and come back to it.
Moving onto the charge attack, I realize I need to make some conceptual decisions. How agile do I want the Thwumper to be? While the inspirations were pretty slow and unwieldy I can blame some of that on 1980s special effects(5). I could probably keep its speed at a lumbering 20 and come up with innovative ways to make up for it with special abilities, but I don’t think I’m going to go that route. On the other hand, I could make it a very agile creature, probably with a Climb speed, and have it turn into a potentially bouncing bowling ball kind of thing. I’m not really wanting to go that far in that direction either. I’ll probably stick with a walk speed of 30, a burrow of 20, and possibly a climb (also 20). I have a hard time seeing this creature be able to just have massive bursts of running speed, so I think I might go with the curling into a ball charge.
Rolling Charge. The thwumper launches itself forward across the ground in a line 60 feet long and 10 feet wide, rolling into a ball as it does so. Every creature within that area must make a DC 15 Dexterity saving throw or be knocked prone and take 5d10 bludgeoning damage.
In this case I made the save DC Strength-based. I looked up the Rolling Ball trap in the DMG for some thoughts, and noticed they made it a Dex save with no damage on a success, so I went with that. As an area effect we assume it hits two targets. And while it’s not in the monster creation section, the DMG rules on spell damage say that if you take no damage on a successful save the spell’s damage can be 25% higher for the same level. Total damage of this spell against two targets adds up to 55, and dividing that by 1.25 we get 44 for the effective damage I’m going to plug into the chart. That leaves this as another CR 6 offensive ability. So far that’s 2 out of 3 of offensive abilities are CR 6. That’s perfectly fine, because we could do Offensive CR 6 abilities every round and still hit our creature target CR of 5.
Something that has been rolling around in my mind, with the current concept of the thwump ability, is the idea of stunning the targets. That definitely should make the ability more powerful if it actually prevents characters from acting, but if I have it end at the start of each target’s turn, it will really only stop them from taking reactions. While situationally useful, those situations are going to be rare enough in context of this monster’s normal usage that it isn’t going to raise the CR. Since it really adds some more flavor to the thwump, let’s do it. Also, with that change, Strength no longer makes sense as the save, and we are squarely in the Constitution save territory.
I kind of want to give them immunity or resistance to acid. There’s no really good reason for this. Ankheg’s do acid damage and they aren’t even resistant. But something about it sounds interesting. So I’m going to do it and come up with lore justification later. A single resistance or immunity has no CR effect.
Looking up some monsters with tremorsense, the range is typically 60’ feet, so I’ll go with that. I don’t see any compelling reason to give them darkvision, but pretty much all monstrosities have it, including bulettes, ankhegs, etc, so they’ll get 60’ darkvision.
As I’ve gone through the process, I’ve decided that it’s probably fine if walk speed is 20 ft, given the other things they have; and they don’t need a climb speed.
This step is where you would also be making multiple versions of features if you aren’t sure exactly how you want them to work, or you aren’t sure if the math is going to go how you want it. For example, I could have made a higher damage version of their multiattack routine, or a lower damage version of their Rolling Charge, but I think they will work fine the way they’ve already turned out. This one has coalesced pretty well, but I might end up making multiple versions of things at this step on some later monster.
Those are all the bits and part we need for the Thwumper, so let’s put it all together properly.
Step F Assemble all the components for a desired overall CR. Resources Needed: Monster Statistics by Challenge Rating table, DMG Step 4 of “Creating Quick Monster Stats”, your previous notes.
Now we take all those components we created in Step C and Step D, and put together a monster. Where you have multiple options to work with, you select the ones with the math to give you the CR you want(28). This is also where you will finalize ability scores, hit points, and any derived values.
Notice that at this point, you won’t be referencing the DMG other than to look at that table (and to remind yourself about the Defensive and Offensive CR adjustments in DMG Step 4 if you haven’t internalized it yet.)
Let’s go right down the monster statblock for the Thwumper and fill in everything.
Thwumper
Large monstrosity, unaligned.
AC 18 (natural armor)
For hit points, we’ll need to determine their Constitution score and hit dice. Looking at how it affects the saving throw DCs of their special abilities, I think we want either a +4 or +5 modifier. Comparing it with those other monsters I made notes on in Step C, I’m thinking +4 is what I want, so Constitution 18. As a large creature it uses d10s for HD. And since the range we want it 86-100, we just math it a bit to see which numbers of d10+4s end up in that range. Turns out, there’s only one that does, 10d10s, for 95 hp.
For Dexterity, it ended up back in the lumbering category, and I see it as less agile the the Dex 11 Bulette. The Elephant and Mammoth have Dex 9, and it definitely isn’t any more agile. Let’s just put it at Dex 8, statistically identical but conceptually lower.
I remember now that I left Wisdom at 10 and planned to think about it more later. Later is now. Since the Ankheg and Carrion Crawler had Perception proficiency, I want to make sure that isn’t a universal “bug” thing, or a universal bug-monstrosity thing. I do a quick check on various bug-like monsters, and learn that many do and many don’t. I don’t see perception as being a strong point for the Thwumper, so there is no need to give it proficiency, or increase its Wisdom any further.
HP 95 (10d10 + 40)
Speed 20’, burrow 20’
Str 18
Dex 8
Con 18
Int 1
Wis 10
Cha 6
I liked the idea of damage resistance to acid. Heck, let’s make it immunity and figure out an excuse later.
With no special defensive features, our Defensive CR stays at 4.
To determine the Offensive CR, we need to average the total damage output over three rounds. We’ll assume it uses its special attacks on two of the rounds, and its multiattack routine on one, for an average total damage of 36. That puts us at the CR 5 damage line. Since its damage output actually relies more on saving throws than attack rolls (over the course of three rounds at least) we compare its save DC to the table, and they are on the same line, so no adjustments. That puts its offensive CR at 5. Averaging Defensive CR 4 and Offensive CR 5, rounds to an overall CR 5.
Damage Immunities acid
Senses darkvision 60’, tremorsense 60’, passive Perception 10
Languages –
CR 5
Tunneler. The thwumper can burrow through solid rock at half its burrowing speed and leaves a 10’ wide, 10’ high tunnel in its wake.
Actions
Multiattack. The thwumper makes three attacks: two with its slashing legs and one with its mandibles.
Slashing Leg. Melee weapon attack, +7 to hit, reach 5 ft, , one creature, 8 (1d8 + 4) slashing damage.
Mandibles. Melee weapon attack, +7 to hit, reach 5 ft, one creature, 11 (2d6 +4) slashing damage.
Thwump (Recharge 5-6). The thwumper causes shock waves in the ground in a 10 foot radius. Each creature other than thwumpers on or in the ground in that radius must make a DC 15 Constitution saving throw or take 4d8 bludgeoning damage and be knocked prone, and stunned until the start of their next turn. Creatures that succeed on their saving throw take half as much damage and are not knocked prone.
Rolling Charge (Recharge 6). The thwumper launches itself forward across the ground in a line 60 feet long and 10 feet wide, rolling into a ball as it does so. Every creature within that area must make a DC 15 Dexterity saving throw or be knocked prone and take 5d10 bludgeoning damage.
Shell Defense: While standing on solid ground, the thwumper withdraws into its shell. Until it emerges it gains a +4 to AC and has advantage on Strength and Constitution saving throws. While in its shell its speed is 0 and can’t increase, it has disadvantage on Dexterity saving throws, it can’t take reactions, and the only action it can take is a bonus action to emerge.
Notice that I increased the radius of its thwump to 10’. I don’t think that will break anything, and fits better with what I’m going for. I also made the recharge of the Rolling Charge less than that of the Thwump. This is purely a conceptual choice. While I like giving it that charge ability, and think it works really well for it, I don’t want it to overshadow the thwump that is part of the creature’s original conceived identity.
Now, with those all put together, we can compare the Thwumper against some of the other CR 5 monstrosities we referenced, and see how it feels.
Comparing it to the Bulette, the Thwumper has slightly better defenses, and slightly worse offenses. It is also a lot slower than the Bulette. Compared to the Young Remorhaz, the Thwumper has significantly better defenses, and about equivalent offenses, though the Young Remorhaz is even more punishing on characters attacking it in melee which might push it higher in offense. The Umber Hulk has similar values for defense and offense, but with less flexibility in attacks. It also has a powerful disabling ability it can use basically at will. Since the Thwumper had to round up to get its overall CR 5, we can assume its one the weaker side of its CR. The Thwumper clearly fits as a CR 5 monstrosity. Compared to the other CR 5s, it is stronger than the Young Remorhaz, on par with or slightly weaker than the Bulette, and pretty clearly weaker than the Umber Hulk with its Confusing Gaze.
If I wanted it to be stronger for its CR, I could give it 1 or 2 more HD, which would move its Defensive CR to 5, still keeping it in the same overall CR 5. But comparing it to other monsters, it feels more like I envision the creature to keep its hp where they are.
Mathematically, the Thwumper is complete.
Step G Polish until it shines. Resources Needed: The results of Step F, creativity, experience.
Here is where we take all of that, smooth off any rough edges, polish up the language to read like a proper 5e statblock, and put any lore and/or art we want to go with it.
As we’re doing so, we can make last minute tweaks, or even go back into a previous step and change our design if we aren’t liking how it all looks when we put it together. You want to have a good idea of how the monster looks and functions overall by the time you are done.
For our Thwumper, the only statistical rough edge to smooth is that I’m going to bump up its even 18 Con to the statistically identical 19 Con because I like it better there.
You'll also note that I removed any vestiges of sonic-ness to its thwump attack, and just referenced vibrations, which is really what I was going for all along.
As I was reviewing the final write-up, I decided I wanted to increase the damage on the thwump attack a tad. By raising it from 4d8 to 5d8, the Offensive CR goes up to 6, which doesn't change the overall CR of 5.
I also need a less comical name for the creature and its signature attack, and some skeletal lore(29).
(1) Heh. Let’s see how well I do.
(2) I do not mean that they are simple, 100% straightforward, or that there is no learning curve. Nor do I mean that there aren’t a few rough spots (which I will address as they come up), nor that the presentation in the DMG is done well. But they do what they are primarily designed to do: tell you what the CR of this creature you just made should be, and create monsters that perform approximately at that CR, within a reasonable margin of error. I’m also not claiming that I will perfectly explain it. Feel free to bring up any “What about”s or “You’re totally not addressing”s. Chances are I have taken that into account but I didn’t think to mention it.
(3) Assuming I don’t run out of steam and never get back to it, which happens more often than I would like.
(4) I’m using letters rather than numbers here, so I can refer to the numbered DMG steps with less confusion. Also, as will become obvious, I am not doing it in the exact same order as the DMG does it, because I think my way is more efficient. Nonetheless, I’m using the same math and the same rules.
(5) I’m imagining something like the creatures from The Dark Crystal or The Neverending Story 2.
(6) Before we move forward, you should to know something the book doesn’t explicitly say, and I think might trip some people up. While we are using the “Creating a Monster Stat Block” rather than the insufficient “Creating Quick Monster Stats” rules, “Creating a Monster Stat Block” rules actually are expansions of the other, not pure replacements. You need to read the quick rules first, and you will refer back to them repeatedly.
(7) You might end up moving it up or down by 1 as you get into the details, but if it's a monster you are creating from scratch you probably won’t need to. If you are converting a previous edition monster and want to make sure its CR has a certain relation to monsters of previous editions, or it has an attack that has to do a certain amount of damage for consistency with other monsters, this can become more likely.
(8) Since it’s 2 CR higher than the elephant, I assume we should be imaging the biggest, probably historically inaccurate mammoth we can, rather than the real world ones which probably weren’t 2 CR higher than an elephant.
(9) Those are the order the DMG has them, but you might want to make the list in an order that works better for you.
(10) With my experience, I went back and looked at the table and noted that the hp line that fits the best is the CR 2 line, 86-100 hp, so that’s the value I’m jotting down for hp: 86-100. I wouldn’t have to do that at this point, it just might save me a bit of time later.
(11) Here we’re going to address a rough spot in the rules, the Effective Hit Points Based on Resistances and Immunities table. It’s utter crap. Don’t use it as written. It assumes both that parties will have less ability to overcome damage resistances than is a reasonable assumption, and that characters who can’t overcome damage resistances won’t have any useful way to contribute (and grappling, shoving, or the Help action are a bare minimum of contribution available to anyone). I won’t offer my own replacement for that table yet, both because it’s not finished and because I’m sticking with the rules in the DMG. Just know that if you use those rules the monster will be weaker than its CR indicates.
(12) Vulnerabilities are sort of “advanced design” and you can and should almost never use them unless you have a lot of experience.
(13) Personally, I’d probably give something like this Athletics to help resist grapples and shoves, but I’m not telling people how to make monsters with all my tweaks, I’m going by the book, so no skills unless we decide to give it Perception later.
(14) Not necessary, but it sure speeds things up!
(15) There is of course always the possibility something will change later, and since such changes will likely be for the better, I’ll call that the “happy possibility”.
(16) You’ll notice that even though I said “ballpark only” for some of the things we were figuring out on this step, I actually ended up pretty firm on some things. Once you have a little experience using the system, you learn what things you can and can’t set more firmly at this point. In this creature’s case, it was the AC. It wouldn’t be the same for everything.
(17) This is another rough spot, because they don’t actually tell you how spells affect their defensive CR. If such a spell changes their AC for the duration of the fight, it’s pretty straight forward. For spells that do something else, you need to refer to the Monster Features table to get an idea of what sorts of features adjust the defensive CR in certain ways. For example, the Parry ability which allows a monster to increase their AC against one attack as a reaction increases their effective AC by 1, and the Superior Invisibility Trait, which will impose disadvantage on most attacks against them increases their effective AC by 2. It would be great if there were a table listing specific manipulations like that and how they effect the math, but unfortunately they didn’t give us that.
(18) If you make up your own special traits, you will need to use your own experience and judgment to determine its effect, see note 17. I’m not going to argue with you if you complain about this rough spot.
(19) Another exception is if you are converting a monster or for some other reason already know how much damage it is going to deal, and the ability scores that would affect the attacks or saving throws.
(20) You need to keep that in mind for saving throw DCs. It’s important (at least for me) that the stat used makes sense—you don’t just pick the highest stat because it gives the biggest number. At the same time, you have to fluff it in such a way that you aren’t using an ineffective stat for it, unless it is intended to be something that rarely works in combat that you just turned into an ability for completeness or flavor (which I approve).
(21) See Nimble Escape. This trait is one of the rough spots. It only works as intended for “Forest Archer Goblins”, who can use it to hide behind a tree and take a shot each turn, granting them advantage on all their attacks, and the character disadvantage on all attacks against them. It is significantly weaker in most real game situations, where the goblins might be in melee, or might not be able to hide as easily, etc. However, it does tell us what advantage or disadvantage are worth for monster design: +/-4.
(22) Unfortunately, neither of these are in the Monster Manual, which demonstrates that the more money you give WotC, the more likely you are to be able to figure out how to use the materials you’ve already bought. Hmm.
(23) I put this little caveat in because it can burrow and this shouldn’t work while burrowing.
(24) Advice for running the monster in its write-up should probably tell the DM that this feature is highly situational and shouldn’t be used most of the time.
(25) One of the unstated best practices of monster design is that you should avoid making monsters dependent on a single powerful attack. The reason for this is that it is just too easy for a party to negate that single attack with class features meaning that monster did basically nothing that round. It’s better to make sure they somehow get multiple attacks, even if you need to use bonus actions or reactions to do it. This doesn’t apply to low-level mooks like goblins and orcs and such, and other creatures that are intended to be fought en masse.
(26) Special abilities like this don’t typically add an ability modifier to damage.
(27) This is another rough area in the rules. The same principle would apply if the creature could make multiple attacks in a turn with a prone rider, but the rules don’t account for it. In this case, it doesn’t matter because my creature doesn’t have anyway to attack prone creatures before they have a chance to stand back up.
(28) If you aren’t committed to a specific overall CR, you can just pick the options that give you the math you like best, and take whatever CR you end up with. Theoretically there is a problem with the way the Monster Statistics by Challenge Rating table works. The table depends on your final CR by virtue of using your proficiency bonus (derived from your final CR!) but actually creates the CR at the same time. There is a circular reference that could be a problem. However, I’ve found in practice, since proficiency bonus only changes every 4 CR levels, that that has never actually been a problem. It comes up too rarely to be a significant functionality issue.
(29) I actually prefer lots of lore and multiverse integration on my monsters (2e FTW!), but I’m not going to do that here.