Monster Infighting CR

[Ursus Spelaeus]

How do you figure the level of an encounter when you have two groups of monsters splitting their attention between the party and the other group of monsters?
Let's say, for example, that you have a group of githyanki fighting a mindflayer. The githyanki attack the mindflayer until it's dead, then they attack the party.
How would you even run such an encounter without making it feel non-interactive for the players?

[Inevitability]

A quick fix would be to assume that each group of monsters splits its attention evenly between the party and their other foes. So a battle between the party, four bugbears, and eight orcs would be the same as a battle between the party, two bugbears and four orcs, with the remaining monsters fighting each other.

This, however, does not take into account the monsters that win the monster/monster battle, nor does it work if one side only has one creature (such as your example), and I'm honestly not sure what to do there.

[Flickerdart]

I would do the following:


The initial CR for encounter building purposes should be calculated for all the monsters together - between the mind flayer and the gith, it shouldn't be much more than level+4 in terms of CR.
The actual CR for XP purposes should be calculated after the fact, based on which monsters the PCs actually engaged with.


If you want to make the fight seem more epic than it actually is based on the CR "budget" then add a whole bunch of corpses (or alert them to the battle early and describe lots and lots of people dying as the PCs close in). The fight was totally awesome, the PCs just got there to witness the tail end of it.

[DrMotives]

If you really want to do more math, then the githyanki get share's of the mind flayer's xp, and if any gith get dropped while the flaer is still alive, it takes shares of their xp. But this will reduce the xp the players get, and you may have numbers that seem more fair to you afterwards.

[OldTrees1]

Hm.

Well in that edge case example, the Githyanki is acting like an ally for the first fight and an enemy for the second fight. So you would calculate the party's strength by including the Githyanki as an ally in the encounter vs the Mindflayer. Afterwards the Githyanki and the party are probably equally depleted so use their normal CR (as a separate encounter) to cancel out the equal depletion.

For a 3 sided fight, one would estimate how much enemy A will weaken enemy B and how much enemy B would waste actions on enemy A rather than on the party. Then lower enemy B's estimated CR based upon those factors. Finally calculate the encounter using the new estimated CRs for both enemies.

[Ursus Spelaeus]

If you want to make the fight seem more epic than it actually is based on the CR "budget" then add a whole bunch of corpses (or alert them to the battle early and describe lots and lots of people dying as the PCs close in). The fight was totally awesome, the PCs just got there to witness the tail end of it.

Neat!


Hm.

Well in that edge case example, the Githyanki is acting like an ally for the first fight and an enemy for the second fight. So you would calculate the party's strength by including the Githyanki as an ally in the encounter vs the Mindflayer. Afterwards the Githyanki and the party are probably equally depleted so use their normal CR (as a separate encounter) to cancel out the equal depletion


I do like battles fought in waves.

Thanks!

[erok0809]

I just did this in a recent game, and Dire_Stirge's method worked wonders. I had the monsters that weren't concerned with the party just fight each other; I didn't even keep track of their initiatives or key stats. Then when the party was finished with the monsters that were paying attention to them, there was only one dude left from the enemies that didn't matter, who ran away. The party received XP for only the monsters they fought. It worked great, and was a fun battle for all.

[Ursus Spelaeus]

I just did this in a recent game, and Dire_Stirge's method worked wonders. I had the monsters that weren't concerned with the party just fight each other; I didn't even keep track of their initiatives or key stats. Then when the party was finished with the monsters that were paying attention to them, there was only one dude left from the enemies that didn't matter, who ran away. The party received XP for only the monsters they fought. It worked great, and was a fun battle for all.

Coo. So was it a bit more handwavy then? Or did you actually roll for the monster's attacks and keep track of their positioning?

[ericgrau]

I'd subtract the monster CR for difficulty purposes, remembering that every +2 CR is actually a doubling. So CR 5 - CR 3 = CR 3 not CR 2. Because a CR 5 is double a CR 3, so take away one CR 3 and that leaves a CR 3.

For xp purposes I'd go with whatever actually survives the fight and estimate the CR of that.

Also keep in mind when planning that randomness could change what the party actually faces. So don't count on the PCs actually facing a CR 3 fight in the above example. Bear in mind that they might face a CR 4 or CR 2, maybe even CR 5 with extreme luck, and consider if that will be overwhelming.