Some of the monster creation rules for calculating damage, damage per round, and offensive CR are confusing me. Help?
TL;DR: Why does it seem like every monster I check has a much lower damage per round than its stat block suggests for calculating offensive CR? Also, where do some of these numbers come from?
I'm looking at an ancient red dragon, just for an example. My problem is with a discrepancy between the DMG's CR table for Offensive CR damage per round, how much damage per round the dragon does, and why its damage numbers are what they are. I'm trying to understand this so I calculate properly how to make my own monsters.
The ancient red dragon does a multiattack. That's 21+ 14 from its bite (35 total), and 17x2 (34) from its claws (69 total, nice). I'm not sure how the extra fire damage is arrived at, though. Arbitrarily, but not counting ability scores? Then it has legendary actions, so let's say it does a wing attack (17), and a tail attack (19). That's 105 damage that round. But it has other attacks, so we need to get a 3 turn average. Maybe next turn, it does fire breath, but that's a lot of variables. 91 damage, but maybe only 2 players in the AoE, and no guarantee of full damage. Hard to be sure. So, on average, this dragon is probably putting out somewhere in the wheelhouse of 105 damage per round anyway, unless I (probably) missed something.
The DMG says that 105 damage per round is appropriate for a Offensive CR of 17. That's 7 CR below the Ancient Red Dragon CR of 24. The dragon's HP is spot on for CR 24, but it does have 22 AC, which is a bit higher than the CR 24+ of 19. But not 7 CR higher, right? What is the justification for putting the dragon's DPR so much lower, and how would I apply that calculation to my own monsters? This seems to be the case with every single monster I look at, that its damage per round is much lower on the stat block than on the offensive CR table. Which means I'm fundamentally misunderstanding something about the process.
Also, the dragon's multiattack is 2d10+10, 2d6+10, and 2d8+10 for bite, claw, and tail. The dragon is gargantuan. Isn't the number of dice multiplied by its size? 1d10 medium, 2d10 large, 3d10 huge, 4d10 gargantuan? That might make up the difference, but I doubt it's miscalculated, I'm probably just off somewhere.
Thanks in advance if you post something to help me untangle this mess and start making monsters.
EDIT: Solved. The attack bonus being significantly higher bumped the dragon's offensive CR up a lot, and having to calculate for an average amount of targets in an AoE changed the damage values, making DPR higher with legendary actions. In other examples given in the comments, a monster's death trait is assumed to count for damage within the 3 turn average, and when factoring in the boost from a difference in attack bonus, the math is more consistent. Thanks all, for your help, I appreciate it.
Posted Sep 16, 2022, 11:56 AM UTC · edited
Over the first three rounds of combat, an ancient red dragon does
Round 1. 239 (2 x fire breath, and 3 x tail attacks), AoE abilities are generally assumed to hit two targets in CR calculations.
Round 2. 126 (1 x bite, 2 x claws, and 3 x tail attacks)
Round 3. 126 (1 x bite, 2 x claws, and 3 x tail attacks)
It's three round average for damage is therefore 164 damage which gives it an initial offensive CR of 22. The normal attack bonus for CR 22 is +11 but the dragon has +17 to hit, so it's CR increases by 3 ([17 - 11]/2) for a final offensive CR of 25.
If you're wanting to check your work, I've calculated CRs for all of the monsters in the Basic Rules. Here's a spreadsheet showing my calculations.
That's a hell of a spreadsheet, thanks for providing it!
Thanks. I have a bigger one with monsters from other official books that I use for analyzing monsters on my site, but I unfortunately can't share that one due to copyright reasons (the sheet parses a lot of info from full monster statblocks).
So one of the things I'm missing is that if I build a monster to have STR or DEX stats for its primary 'to hit' roll, and that deviates from the average for a monster's CR, that this dramatically increases its offensive CR, and this is why damage is lower to compensate?
That would imply that I should only create the correct (damage-based) ability scores by estimating the amount of damage that I would like to do with an attack, then working backwards until I get the ability modifier that I need to do that damage, and then write in the ability score based on the modifier I get from the calculations. Is that accurate?
It's more complicated than that. Encounter math is based on XP, and a creature's XP is the product of their effective hit points and effective damage per round (if you're interested, I have a fully derivation of this here, but fair warning, it's pretty math heavy). Challenge ratings are just classifications of monsters worth similar amounts of XP. So, while monster hit points, armor class, saving throw bonuses, DPR, and attack bonus within a given CR might vary, the total product should be close to target. A creature could have high AC and high AB with low HP and DPR to compensate, or high AC and HP but low AB and DPR. This is why you need to look at the whole picture to assess if the CR makes sense.
Don't all creatures of the same CR give the same XP? So then aren't XP and CR essentially the same?
Yep, in terms of how they're presented in the rules they're the same, but that's just a classification. Just like some monsters are slightly tougher or weaker than average for their CR, some are actually worth slightly more or less XP than the value listed in their stat block. The difference generally aren't too big, though, which means the encounter math still works well enough.
During the DnD Next open playtest for 5e, monsters of the same CR (or level, as it was called then) actually did have different XP values from one another. I can't say for certain why WotC moved away from this for the official release of 5e, but my guess is it was done for the sake of simplicity to make calculating encounter difficulties slightly easier.