D&D 5E CR and Encounter Difficulty: Is It Consistently Wrong?

[Fanaelialae]

That's really a problem inherent to the whole "level up by fighting things" system, not to XP multipliers per se. When going by RAW (no multipliers for large groups), the optimal strategy for level-grinding is to fight things one at a time, either by seeking out monsters in dungeons (or random encounters) or, even better, by summoning Allosaurs via Conjure Animals and ordering them to try to kill you, one at a time. Each 3rd level spell slot becomes 450 XP per day. (And yes, summoned creatures do count for XP per MM guidelines.) Even better, tell it to kill your buddy who is 600 feet away and armed with a longbow. Since you can't maximize reward, minimize risk by controlling the scenario.

Granting XP for killing things leads to gamification of the game universe. It leads to PCs viewing dangerous creatures as a resource to be exploited, random encounters as a fun bonus instead of a threat, and crazy thrill-seeking behavior. This isn't necessarily a bad thing, since ultimately it is a game, but it is an oddity.

If you grant extra XP for harder encounters, expect to see certain PCs going into battle blindfolded and naked, fighting with their off-hand, in order to make the fights more "difficult" and thus more efficiently exploit the resource.

I don't see it as a problem really, just a quirk.

Though I'd never allow my group to level up by summoning things. I would rule that summoned creatures count for XP only if an enemy summons them. I don't consider 5e an edition meant to be bound by legalese, so I believe it's fair.

I have to admit, I probably would grant extra XP if the PCs went into battle blindfolded and naked. Probably just the first time they tried it, but the amusement factor ought to be worth something.

 

[pemerton]

Another left-over assumption: that there is supposed to be one encounter per long rest.

In what edition of D&D was that an assumption?

 

[pemerton]

I think the primary reason that Mistwell is unwilling to accept using CR for encounter building is because the encounter building rules are entirely incompatible with CR. There is no way that I can see to modify the XP budgets to accomodate using CR.

Yes, XP values are based on the CR of the monster. However, there is no reliable equation for determining a creature's XP from CR or vice versa.

There is no reliable equation for determining a creature's XP from CR or vice versa, and encounter difficulty CANNOT account for CR in adjustments.

This was covered in more detail by [MENTION=13120]eryndel[/MENTION] upthread. The fact that there is no simple function defined over the real numbers that relates CR to XP (or vice versa) doesn't mean that the two are not related.

XP is a value that is read off CR via a table provided in the core rules.

It's used as a warning light to tell the DM to look closer at the monster relative to the party and see if there is something that would be unusually difficult based on that monster and party, such as immunity to spells below level 6 with a party that only has spells of level 6 or lower. It's not the overall determiner of lethality, just a special kind for that sort of issue. General lethality is determined by the XP budget and encounter difficulty chart - which is purely XP based and does not use CR at all.

CR is also used to determine the XP value of a monster - see the chart on pages 61 to 62 of the Basic DM PDF. So the input into the encounter-building guidelines - namely, monster XP values - is itself derived from CR. Which is, in turn, derived via the monster-building guidelines others have referred to plus (it seems) a hefty does of eyeballing.

Hence, when people say that "CR is broken for encounter building purposes", what they are saying is that the XP values that have been assigned to monsters on the basis of their CR do not provide an accurate guide to encounter threat levels. They may also be implying that the suggested difficulty multipliers are not very reliable.

Such claims may be true or false, but that truth or falsity will depend upon whether or not the XP values when aded and multiplied as the guidelines suggest do, roughly, correlate to encounter difficulty. The terminological issue is a total red herring, in general and in the context of this thread. I have read the whole thread, and have not seen a single post from anyone confused about how the encounter building guidelines work, how CR is related to monster XP value, or how CR is related to a monster's mechanical capabilities.

On the substantive issue, my view is that the guidelines very obviously must break down at some point: whether a Giant Ape (CR 7, 2900 XP) is as challenging as 15 Acolytes (CR 1/4, so 50 XP each, x4 for numbers = 3000 XP) will depend so heavily on tactical context, party composition, etc that the comparison runs the risk of arbitrariness.

If the guidelines break down even in simple cases - say, when comparing a Giant Ape to a Mummy and a Ghost haunting a tomb (CR 3, 700 XP plus CR 4, 1100 XP, x1.5 for two monsters = 2700 XP) - then that's a bigger issue. For a mid-level party without magic weapons I think the undead look harder than the ape, but I haven't actually run the encounters to compare.

 

[Grazzt]

Though I'd never allow my group to level up by summoning things. I would rule that summoned creatures count for XP only if an enemy summons them. I don't consider 5e an edition meant to be bound by legalese, so I believe it's fair.

I wouldn't allow it either. First character that tries it gets a horde of red dragons dropped on their head. (And no edition is bound by legalese; it's bound by what the DM says is allowed/not allowed.)

 

[pemerton]

On "difficulty multipliers" and arbitrariness:, Gygax had this to say in his DMG (p 84), although he was talking about actual XP reward being multiplied by difficulty, not just using adjusted XPs for purposes of encounter balancing:

The judgment factor is inecsapable with respect to weighting experience . . .

With respect to monsters, each hit die balances 1 experience level . . . If the numerator [monster HD] is greater than the denominator [total levels of all participating PCs] then full experience should be awarded. If the denominator is greater, use the fraction to ajdust the amount of experience by simple multiplication. . . .

12 orcs are not equal to a wizard! . . . Therefore, the following rule applies:

If the average hit dice or level is 10 times greater than the average level or hit dice, there must be an adjustment of at least halving or doubling the experience point (x.p.) award as the circumstances dictate, except if the lesser group is approximately 20 time more numerous than the greater value group.

(20 orcs might prove troublesome to a wizard, but even that is subject to the circumstances of the encounter.)​

Page 85 sets out similar guidelines for reducing the XP value of treasure taken from guardians that are relatively weaker than the PCs.

There is a clear recognition that encounter difficulty depends not just on numbers but upon party composition - in particular, reliable AoE attacks (which are the stock-in-trade of the AD&D wizard) make even large numbers of low-level monsters relatively easy to defeat.

I also think it's interesting that he doesn't factor in the balance of numbers until the ratio reaches 20:1. Otherwise it's just a straight comparison of levels/HD. This is closer to 4e than 5e (because in 4e you just add XP values, don't factor in numbers, and will almost never be reaching ratios of 20:1 unless using minions, who are designed to be used only in numbers in any event).

Someone on these boards worked out a system for eliminating the numbers multiplier from 5e, by instead reducing the XP values of higher-CR monsters relative to lower ones, meaning (speaking roughly) that you had to add fewer low-CR monsters together to reach the higher-CR equivalent encounter values. But I can't now remember the name of the poster or the thread.

 

[DaveDash]

There is a clear undeniable relationship between CR and encounter guideline building, the fact people are trying to deny this is baffling.

The monster manual makes the base assumption that the relationship between CR and encounter difficulty is that one monster of CR equal to the parties level should be a 'challenging' encounter for 4 party members.

So based on that assumption, how does CR directly relate to the encounter building guideline XP budgets?

This is how they relate:




This table illustrates what happens when you take a monster of CR equal to the party level (against 4 party members), and divide the encounter budget by how many monsters of that CR are expected in that encounter.
Apart from the fact there is a CLEAR relationship, this also tells you:

To get an easy encounter to use roughly half a monster of CR equal to the party level.
To get a medium encounter you use roughly 1 monster of CR equal to the party level.
To get a hard encounter you use roughly 1.5 monsters of CR equal to the party level.
To get a deadly encounter you use roughly 2 monsters of CR equal to the party level.

And this probably explains why the whole encounter building guidelines are so messed up. 2xCR1 monsters against a 1st level party WILL be deadly. 2xCR20 monsters against a 20th level party will be a cakewalk.

 

[I'm A Banana]

In what edition of D&D was that an assumption?

3e, at least as it was practiced at many tables, had "HERE IS THIS BIG MONSTER AT +3 CR! RAAAR! Okay, now you can rest."

Earlier e's, with the slow healing and the unreliable magical healing, were also accommodating to that style (a long rest wouldn't heal you much, so it's OK if you can sleep after a fight with a big monster, your resources were still being drained).

4e wasn't as comfortable with that mode of play, but I did see DM's doing it (largely because it's an easy default and because characters can still die in a single 4e encounter despite having a pile of resources left un-used).

So to varying degrees at different tables, it's ALWAYS been an assumption.

Heck, it even got lampshaded in OotS.

5e's a little different in that if you do that, and you want that one encounter to be "hard," it might not be as hard as you think it is. Unlike 4e, the party can bring most of their resources to bear at once. Unlike 2e and earlier, your natural healing is plentiful enough that you'll be nearly at full HP (if not full HD) after one night's sleep. Unlike 3e, CR doesn't try to tell you the average level of challenge, but rather is a "you must be this tall to ride" sign, and the XP budgets in 5e presume multiple encounters in an adventuring day.

It's something you can do in 5e, but the designers didn't really explain well how you might do that, or what might be required if you want that, which is, I imagine, catching a number of DMs on the back end, when the party rips through their one over-land encounter by nova-ing and they don't have more than one encounter, making the party seem to sail through even supposedly-deadly encounters.

 

[Cernor]

There is a clear undeniable relationship between CR and encounter guideline building, the fact people are trying to deny this is baffling.

People aren't trying to deny that there's a relationship, but by far the more important factor is XP and numbers of foes, and you prove that yourself.

The monster manual makes the base assumption that the relationship between CR and encounter difficulty is that one monster of CR equal to the parties level should be a 'challenging' encounter for 4 party members.

This table illustrates what happens when you take a monster of CR equal to the party level (against 4 party members), and divide the encounter budget by how many monsters of that CR are expected in that encounter.
Apart from the fact there is a CLEAR relationship, this also tells you:

To get an easy encounter to use roughly half a monster of CR equal to the party level.
To get a medium encounter you use roughly 1 monster of CR equal to the party level.
To get a hard encounter you use roughly 1.5 monsters of CR equal to the party level.
To get a deadly encounter you use roughly 2 monsters of CR equal to the party level.

Alright: let's start with the MM's assumption and work our way down from there. The only assumption the MM makes is that "An appropriately equipped and well-rested party of four adventurers should be able to defeat a monster that has a challenge rating equal to its level without suffering any deaths." That's it. In the example provided it says the monster should be "a worthy challenge", but what does that mean? Should it be a medium encounter, to account for the fact that there should be no casualties? Perhaps it should be a hard encounter, to account for the fact that nobody should die, but the threat should be there if there's a particularly bad streak of the dice?

Personally I'd tend towards it being a hard encounter, because it says they shouldn't suffer any deaths (leaving the possibility open) and the description of a hard encounter says "[In a hard encounter] there's a slim chance that one or more characters might die". If so, then the only metric that matters is the one in the seventh column in your table: the number of CR-equivalent monsters required to make an encounter "hard". If not, then what are you looking for in your table?

Now we can look at the table. It's fascinating, really. Using the experience guidelines from the DMG (see, even if you think CR is an equivalent for XP you still use the XP rather than CR value), we can see how many monsters of a CR equal to level are required to make each difficulty of encounter for your hypothetical party. Level 1 is relatively clear-cut: "You need 1 monster of CR 1 to provide a medium challenge for a party of four 1st-level adventurers". Levels 2 through 20 are considerably less so. "You need 1.11 (repeated) monsters of CR 5 to provide a medium challenge for a party of four 5th-level adventurers". What does that mean? How am I supposed to find 1.11 repeated monsters? Perhaps an ooze is 1.11 times bigger than normal? Maybe a marilith has 1.11 times as many arms as a normal one? Maybe it instead means that I have to throw a monster of CR 5.55 repeated at the party?

This table goes to illustrate that CR is useless in terms of determining the difficulty of a given encounter. Why? Because a monster of CR 5-7 is an easy encounter for a party of 4 level-appropriate adventurers, while at every other level, a level-appropriate monster is a medium encounter; if CR was a reliable indicator of a monster's strength against an equal-level party, it would be consistent from 1-20, and lie in the same region of a "medium" encounter (ie they're all medium tending towards easy, or medium tending towards hard). What if I wanted to throw a CR 5 monster at a 4th-level party? The CR can't account for that, so I'd have to look at the XP values to see where it would come on the tables (and so XP>CR). What if I'm tired of throwing enemies at my players one at a time? The CR can't account for that, so I'd have to look at the XP values and start using the multipliers to figure out the correct number of enemies, as well as the CR of those enemies, in the encounter (and yet again, XP>CR).

CR, XP, and numbers of monsters must be integers. If you need to use "roughly half a monster of CR equal to the party level" to make an easy encounter, does that mean I cut a bugbear in half to make a 1st-level party have an easy fight with it? Should I use the top half or bottom? Perhaps you should simply use a monster of half the intended CR, then. This works at level 1 (one CR 1/2 monster), but once you reach, say, CR 6, this doesn't work in the slightest: a CR 3 monster is nowhere near half the XP given by a CR 6 monster, and the discrepancy gets larger as you progress up the table.

And this probably explains why the whole encounter building guidelines are so messed up. 2xCR1 monsters against a 1st level party WILL be deadly. 2xCR20 monsters against a 20th level party will be a cakewalk.

Yeah... No. The encounter building guidelines are messed up if you use them without the assumptions they make for determining a party's power. If you use them correctly, they seem to work perfectly fine.

 

[Joe Liker]

I don't care that much about the inexact nature of CR. My main concern is awarding appropriate XP, and the guidelines in the rules are wholly inadequate for that. I always award bonus XP when the party is outnumbered because that's always a harder fight.

There's also no such thing as "no XP for low-level monsters" in my game because all monsters pose a threat under bounded accuracy. The tiny amount of XP they are naturally worth (due to low CR) is penalty enough.

For my multiplier, I use a formula based on a previous version of the XP multiplier. It actually subtracts XP when the party outnumbers the enemy, which I think is completely appropriate.

[0.5 * (E - P) / P] + 1

where E = number of enemies, P = number of party members.

So far, the adjustment always lands me in a place that feels fair for the encounter difficulty. By that, I mean looking back after the fight, the adjusted XP reward seems right for the effort that was empirically required.

This also addresses the "one lich, three skeletons" problem because an encounter with four monsters is going to have an XP multiplier of 1 (assuming a 4-player party). If there are seven or eleven skeletons, the multiplier does increase, but that many skeletons really are going to make it harder to kill the lich, so I'm not bothered at all.

 

[Fanaelialae]

I wouldn't allow it either. First character that tries it gets a horde of red dragons dropped on their head. (And no edition is bound by legalese; it's bound by what the DM says is allowed/not allowed.)

That's true, Rule Zero always applies, but some games have more legalese than others. The tone of 5e says to me that the designers intend for players to abide by the spirit (as adjudicated by the DM), rather than the letter, of the rules. I'd expound and name editions, but I'd rather not spark an edition war.