Trouble with CR system

[atemu1234]

I was running a half-dragon Vaath (upped to a dozen HD) against a group of tenth-level adventurers. I thought they could handle it (there were six of them) but they wound up getting nearly killed before running off. I had it get tricked into sleeping by the bard, but I felt sort of bad for putting them through that. So I started thinking, what's a safe CR for a larger-than-average group?

[RustyArmor]

I always have trouble with it as well. Group sizes, Optimizers, and even good/bad luck. Just vary to much to give stuff a easy to pin down CR. Mostly I just go with my gut or alter a monster accordingly.

[tyckspoon]

CR is dysfunctional at just about everything it tries to do, unfortunately. Good idea, but the game was built with too much variety to make it work. I will give the usual advice, tho, and it's even more relevant for a larger party size - don't use single big monster encounters as your standard fight template. Either they have much stronger defenses/offenses than the party and they become a much more difficult fight than intended (especially likely if you're using something like CR of party level +2 or so to adjust for the larger group) or they don't have the power they need to stand up to numbers and they get swamped under the action economy disadvantage. Try to develop your encounters with at least two opponents, more is better.. 4 weaker enemies can be a better challenge than one big bruiser, and it helps bring out the tactical side of the rules (in a party of 6, I'm betting there's at least a couple of players who would really appreciate that.)

[eggynack]

There really isn't necessarily some safe CR. You obviously have variance in the group's power level, for the reasons noted, but there's also a lot of variance within a given CR. My favorite example is that a riding dog has a CR of one, while a first level druid, which has a riding dog animal companion that is wearing leather barding, also has a CR of one. It's just an odd and illogical thing, and there are examples simultaneously less obvious and more extreme than that. Just take a look at the allip (http://www.d20srd.org/srd/monsters/allip.htm) as an example, also known as the creature capable of singlehandedly taking down the tarrasque (http://www.d20srd.org/srd/monsters/tarrasque.htm). It's tricky stuff.

[John Longarrow]

For groups over 5, I normally use 2 monsters who's CR = average party ECL-1. This avoids the whole "One big monster too hard to beat" problem that higher CRs get while avoiding the "Gank the monster" problem large groups tend to have through action economy.

I also like tossing in a bunch of weaker creatures for fluff and as mobile terrain. This tends to reward good tactics by the party while punishing bad tactics.

[OldTrees1]

I have found that 6 PCs can take care of CRs 1 greater than 4 PCs can take.

[Amphetryon]

The CR system is swingy and buggy to begin with, but the more PCs in the party, the swingy-er and buggier it gets, because the effective party level doesn't improve at the same rate as the CR system. This, in turn, is due to the way the action economy tilts more and more in favor of the larger group. Putting a by-the-book CR appropriate single enemy against such a group is quite likely to result in the enemy getting all but destroyed before he can act, or in the enemy wiping out one or more party members if he gets the Initiative. This is why I generally find it better to use multiple enemies at a lower CR to oppose big groups.

[Ssalarn]

Just to throw my voice in with everyone else's, the best way to keep CR as balanced as possible is to keep the action economy as balanced as possible. Instead of raising the CR of the encounter by throwing single more powerful enemies, who may be able to wipe the enitre party with a single AoE, add in more mooks or an additional critter with a different role than the BBEG. If it was a standard encounter, like 6 goblins intended to challenge a party of 4 adventurers and you're running a party of 6, add in 1 more goblin with a level of adept, druid, or bard.

[Kudaku]

Think of the CR rating system as a tree. The branches on the left side of the tree represents groups that optimize and synergize less than expected, and the right side of the tree represents groups that optimize or synergize more than expected. The age and size of the tree represents the expected competence of a party of the appropriate level.

When the party is low level and your tree looks like (http://thumbs.dreamstime.com/z/small-tree-2537936.jpg) this, there isn't that much distance between the left and right branches, and the CR system is fairly reliable - you can only do so much to optimize or screw up a level 1 character, so the gap isn't too large.

When your party are at level 10, the tree looks like this (http://vbaudoin.files.wordpress.com/2009/07/0219-002-angel-oak.jpg). Challenge Rating fails completely at covering the gap between the left and right branches, or low and high op groups.

I generally find that the best way to balance encounters for parties is to eyeball it and use CR more as a loose guideline than a rule. A party loaded with THF Power Attack enthusiasts will likely struggle with a flying enemy, while a party loaded with archers can be completely stomped by an enemy with DR 10/Slashing. Reverse the encounters and they'll likely both have an easy time.

I also agree with Ssalarn's advice on action economy - it's better to have multiple moderately dangerous creatures than one Big Bad. 6 PCs will demolish most CR-appropriate solitary encounters because of how many actions they get.

[Urpriest]

In this case I think you're just facing a fluke. Unless you optimized its feats and gear, a Half-Dragon 12HD Vaath is not that scary, and should not have been difficult enough to rout a six-person 10th level party, especially alone. An Adult White Dragon is the same CR and more dangerous in basically every way.