Shardstone
Hero
Getting to 10th level (in Odyssey) should take the same amount of XP as getting to 5th level (in 5E).
D&D 5E Fixing Challenge Rating
Orange Mage
Explorer
Without any further feedback from Mike Mearls about this, I'm going to use the 5E DMG's 'Encounter Multipliers' table to adjust CP to allow for groups of monsters, as a start.
Actions in combat are certainly important, but that table as an encounter calculator vastly over values multiple creatures. I wouldn't rely to heavily on it.
Orange Mage
Explorer
Tomedunn's calculations suggest that the table undervalues multiple creatures, unless the party members can reliably deal damage to multiple monsters with single actions.
White room calculations do not usually reflect actual play, in my experience. I have been running 5E for a long time and the difficulty increases given by the table have never materialized.
Orange Mage
Explorer
That's interesting! Have you made any record of your experiences? It would be great to have some real-play statistics (including party composition).
A creature that acts twice and deals 10 damage per action isn't substantially different than a creature that acts once, and does 20 damage on that action.
"Action Economy" matters when actions don't deal damage, and various forms of action nullification that scales better on fewer targets.
Like, if you can take a creature and say "you don't act next turn" as your action; then it doesn't matter if their action would do 1 billion damage, you just traded your action for theirs. But even in softer cases, like "I knocked you prone and pushed you 30' away" - the target gets to do an action, but it is reduced in scope and choice. Or even "I used my action to give all my allies advantage" - the more creatures on your side you have, the lower that cost is and the bigger the boost.
But most of the impact of why 2 monsters is more dangerous than 1 is that a natural way to measure a monster is its level. And if HP and damage are roughly proportional to level, then two level 5 monsters are going to each have half the HP and half the damage of a level 10 monster. If the level 5 monster fights the level 10 monster one-on-one, it will only drain 1/4 of the level 10 monster's HP -- but if it is 2:1 it goes up to 3/4 of the level 10 monster's HP. Twice as many monsters made that side 3 times as dangerous!
This comes from the fact that scaling both offence and defence has a quadratic impact on power, not a linear one, but we treated it as if it was linear. When you group monsters, the impact is not quite quadratic, because groups of monsters are subject to attrition in combat. A decent naive model is that the groups of monsters are subject to a triangular-shaped attrition over combat, with the other side focus-firing down one and eliminating it then moving onto the next.
Another model is to assume the other side uses AOE damage, or a combination of focus fire and AOE. As it happens you can model sub-one-shot AOE damage as doing focus fire damage to 1 target, and 0.5x value damage to all secondary targets, and you get a very similar amounts of total enemy damage done - ie, you can change how you model AOE damage, and it starts behaving (model-wise) as if it was single-target damage.
Like, you have 3 monsters each with 5 HP. You do 1 HP per attack. You take 3*5 + 2*5 + 1*5 damage, a total of 30. You add someone able to do 1 point of AOE damage at the start of the fight. You now take 3*4+2*4+1*4 = a total of 24 damage. Alternatively, you add someone who does 2 points of single target damage at the start of the fight. You now take 3*3+2*5+1*5 a total of ... 24 damage. The 2 points of focus-fire damage had the same impact as 1 point of aoe damage on 3 targets - 1 point on primary target, plus 2 * 0.5 on secondary targets = 2 points of effectiveness.
That 1x on primary 0.5 on secondary happens to fall out of the math of the area of a discrete triangle. I'd been using it as a heuristic for a while before I realized it was actually sound and grounded in the math, which amused me.
tomedunn
Explorer
As an addendum to that point, my analysis of XP thresholds for PCs shows that martial classes, which typically don't have strong AoE capabilities, tend to have higher XP values for the purposes of encounter balancing. So for a martial heavy party, even if the encounter multiplier is underestimating the monster side of the equation, the XP thresholds for the PCs are likely underestimating their side of the equation as well.
The model I developed is more of an approximation than a white room calculation. There are parameters in it that you can use to control the level of "slop" in the encounter, including how strong a group's AoE capabilities are as well as how efficiently they can deal AoE damage. That said, if you keep track of how much damage your party takes relative to their maximum HP for your encounters, you should be able to use the results to calibrate the model to your own party.
The statistical nature of DnD combat means you'd need a pretty large number of encounters to do so accurately, which may not be practical for most DMs. My hope is that once DnD Beyond get's their maps and encounter tools fully operational that WotC will be able to collect that kind of data to better calibrate these kinds of systems in the future.
The higher level you go the more I find this not to be true. More attacks is much better.
1) post 5th levels PCs very rarely die to damage, they die to death saves (or auto fails due to hits taken).
A creature with 3 attacks can drop a pc, then go crit crit, and that character is dead. In contrast a monster that does 4x the damage in one attack is far less scary.
2) PCs have all sorts of things thst can mess up a single attack, fewer that mess with all attacks in the round. More attacks means more chance to get damage done.
3) being able to sub out an attack for a grapple let’s say isn’t bad when it’s only half or a third of your damage. When it’s all your damage…hard to justify.
Again, in my experience, more monsters tends to extend fights, which increases the number of dice rolled, which increases the probability of non average results (critical, very high or very low damage, failed saves) but it doesn't actually increase difficulty-- at least not to the extent that the chart suggests.
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