D&D 5E 5E Maths

[Morrus]

Are you familiar enough with 5E's design to explain to others how to make a monster? I'd like to include design advice in the Monster Database (see the Databases menu in the top navbar).

What advice or mathematical calculations would you add? How is a skill, attack, or save calculated? How do you arrive at a CR? That sort of thing.

So --

1) What 5E design questions do you have? Monsters, spells, anything?

2) What are your answers to these?

 

[Zardnaar]

So far I have been tweaking existing monsters a little bit and I might swap out a power for a class ability. Take the NPC Knight in the playtest documents. I dumped the buff trait they get and gave the part of the mounted feat which gives them advantage vs opponents smaller than their mount. Exchanging a trait for something like a weapon style seems fine as well. Switching out spells can be done as well but taking away cure and adding inflict can do bad things to PCs as a priest or acolyte now has a 3d10 damage spell.

 

[DLIMedia]

Most of this is reasonably documented in the DM's Basic Rules available for free on the WotC site, and the DMG will reportedly contain more information regarding it.

Of all the math involves, what really gets me is how to calculate a monster's Challenge Rating. There really is no easy way to do that, and short of playtesting or simulating it there's no definitive way to determine how much a threat a monster will pose to the PCs and how much XP it's worth.

 

[dd.stevenson]

How do I design kick-ass lair actions? That's the big one.

 

[jadrax]

Of all the math involves, what really gets me is how to calculate a monster's Challenge Rating. There really is no easy way to do that, and short of playtesting or simulating it there's no definitive way to determine how much a threat a monster will pose to the PCs and how much XP it's worth.

The worst thing about working out Challenge Rating is the proficiency Bonus is keyed of it, so you end up going round in a circle trying to pin down the exact numbers.

 

[Grazzt]

Are you familiar enough with 5E's design to explain to others how to make a monster? I'd like to include design advice in the Monster Database (see the Databases menu in the top navbar).

What advice or mathematical calculations would you add? How is a skill, attack, or save calculated? How do you arrive at a CR? That sort of thing.

So --

1) What 5E design questions do you have? Monsters, spells, anything?

2) What are your answers to these?

Definitely add the "How do you figure attack bonus, saves, skills, etc.

Skills, attacks, and saves are ability bonus + proficiency bonus. Prof. bonus is based on CR not the monster's Hit Dice.

Some monsters have expertise on skills or saves (similar to the rogue's ability; add double the prof. bonus to the skill or save). If it makes sense that the monster has really good senses, or is really good at hiding or sneaking, or is really good at resisting poisons, diseases, etc...it probably has double it's prof. on the save or skill. Doesn't seem to be a pattern (all beasts have this or all monstrosities have that....if it makes sense for the monster, it has it)

CR appears to influence hit points, AC, expected damage output, and some other things. (I've taken all the monsters released thus far and dumped AC, HD, hp, attack, damage output, and some other stuff into Excel; there are ranges and patterns the monsters fall into). I believe when we get the rules for monster creation (DMG I hear), we will see something similar to (or a blend of) the Pathfinder monster creation table and the monster creation chart from 4e.

HP are figured as in 3.x or PF. (HD X avg of die type) + (Con bonus X Hit Dice)

Hit Dice for monsters appear really be nothing more than a way to arrive at the range of HP appropriate to the monster's CR. Hit Dice are based on size (d4 Tiny, d6 Small, d8 Medium, d10 Large, d12 Huge, d20 Gargantuan). They don't govern saves, skills, or attack bonus any more.

Monster type appears to no longer includes a laundry list of specific abilities, resistances, weaknesses, etc. Like in 3.x where all magical beasts had this, this, this, and this. Or all mindless undead were immune to mind-affecting effects. There are some that seem to kinda follow a pattern (demons and devils and their resistances for example), but some don't (like being able to charm what used to be vermin or used to be mindless undead). Some former vermin or mindless may be immune to being charmed or frightened or whatever, but some may not.

Spell attack and save DC appear to follow the same formula as PCs.

Save DCs for monsters. Some (like grapples IIRC) appear as DC 10 + Str modifier. Other save DCs (again IIRC) appear to be DC 10 + prof bonus (or maybe Con bonus, I don't recall at the moment).

 

[Grazzt]

Most of this is reasonably documented in the DM's Basic Rules available for free on the WotC site, and the DMG will reportedly contain more information regarding it.

Of all the math involves, what really gets me is how to calculate a monster's Challenge Rating. There really is no easy way to do that, and short of playtesting or simulating it there's no definitive way to determine how much a threat a monster will pose to the PCs and how much XP it's worth.

Once the DMG comes out, it'll obviously be easier.

One thing you can do for now is design or convert your monster. Look at it's hit point total after converting to 5e. Find a few monsters in the DM Basic Rules around the same HP. Look at their CR. Set your monster's CR to that. Then look at several monsters damage output for that CR (like if you peg your monster at CR 2, grab a bunch of CR 2 monsters and look at their damage output in a given round). Set your monster's damage output close to or just above that by increasing or decreasing its damage die type or giving it the multiattack ability. (Even if, say in the case of an NPC, it really couldn't make multiple attacks per round. WotC does this. There are several examples of low level NPCs making multiple melee attacks in a given round.)

For example, if you look at a bunch of CR 2 monsters and see their average damage seems to be 12 (or whatever) damage per round (from any source; attack damage, attack damage plus fire, spell damage, whatever), then set your CR 2 monster to around that. Increase or decrease some or all attack damage die or secondary damage (fire, cold, acid, whatever), give it multiple attacks per round, etc to bring it's average damage output to the average you found. (If it has other effects that key off it's attacks like stunning or whatever, some monsters seem to do less damage than average for their CR...which makes sense as there's an additional and potentially nasty effect tied to their attack(s)).

Also, look at your monster's AC. Compare it to the AC of a bunch of monsters at the same CR. Most will be around the same range (though there are some outliers, usually the monsters wearing armor). Reduce or increase the monster's total AC (by giving it natural armor, adjusting it's Dex mod, whatever).

 

[Minigiant]

It's not exact math but I see a pattern I call the "Fighter Cap"

Basically a monster's average damage of their nova strike rarely kills a fighter with decent Con whose level equals its CR. So average nova damage on a turn maxes out at 4+8*CR.

There are exceptions (like bugbears and elephants) but I put that as a corollary that it only counts for straight up fight so surprise attacks, crits, charge SoD, and nonstandard damage doesn't count.

Basically, a CR X monster cannot just stand in front an Xth level fighter at full health and drop him without a crit, charge, or surprise attack.
However a Xth level rogue or cleric aint so lucky.

Average multiattack action damage + lair action damage + legendary action damage cannot exceed 4 + CR * 8.

 

[fireinthedust]

Given how much is based off CR, it sounds more practical to start with the desired CR and work from there.

Maybe list abilities you want, then size, pick the CR you want, and fill in the blanks for numbers of dice for damage and Hit Dice?

Just a theoretical strategy for designing them, educated guess based on other games I've run or home-brewed: path of least resistance/guess work.

 

[Tormyr]

Until the DMG comes out, we will only be making guesses. As soon as you increase one of its abilities beyond the average for that CR, something else has to drop. If the AC goes up, the health or attack might go down. Wizards have really low health for their CR. A multiattack can drop the damage below average. There is this wierd balance going on, and I don't know what the criteria are.

What I would say is take something from the MM that is close and replace the traits and attacks and ability scores. If you start with something that is close to what you want, you will be able to keep the same CR or only have to adjust it by 1.