Three character party fight CR

[Steve Danials]

I'm running a mini-campaign/bunch of one-shots for me and a couple others. Right now we're all level 10 - elf maestro (third party class that does a variety of effects via conducting, sorta like a super-bard), human two-weapon fighter with keen kukris, and a oread kineticist with fire/aether.

My question is how should I calculate CR to make a challenging, but not overwhelming, fight? If we get into multiple fights in one day, without recharging/resting and all that, I don't mind *that* - whittling down resources is a fun way to push how well a group has prepared. However, I don't want to accidentally overpower it, and take everyone out, or make it too easy, and have them just waltz through with only scratches.

Story time:

Last night we got into a fight with what I'd hoped would be challenging, but not super deadly: 4 Pugwamgi, two Thin Men, and a Boogeyman. I'll admit, I did away with the Boogeyman's DR 15/Cold Iron, and held off on Phantasmal Killer, because either one would basically render the fighter either next to useless, or f-ing dead (I sincerely regret not suggesting he take Iron Will as he leveled up...).

Fast forward, and the fighter is going toe-to-toe with the Boogeyman, and everything seems to be doing fine. Keeping with the abilities, I had the Boogeyman go invisible, and sneak attack the fighter.

Aaaaand, I crit, leaving the fighter with around 20 HP.

My f-ing kineticist *missed* on his turn, otherwise it wouldn't have been an issue, but the Boogeyman then knocked our fighter down to -1, and, on the next turn, killed the s**% out of him.

I'm still fairly new with DM'ing, so even if it seems like obvious advice, it would be appreciated. Thanks!

[voideternal]

By Boogeyman, do you mean Bogeyman?
If so, a critical hit should be virtually no different than a normal attack because a Bogeyman's attack routine is two claws of 1d8+1 + 6d6 sneak attack, and sneak attack doesn't double on critical hits. After the first sneak attack, the bogeyman should have lost his invisibility, so the second attack would lose sneak attack.

A critical hit from a Bogeyman looks like 2d8+2+6d6, which is average 32 damage or 54 damage on max rolls. At level 10, a Fighter with exceptionally low hp would have roughly 60 hp, but most fighters would probably have around 90 or 100 hp.

You said that the fighter had 20 HP after critical. There are a few ways this could have happened:
1) The fighter did not heal before the battle started. This is tactically the player's fault.
2) The fighter naturally has low maximum hp, and you rolled lucky. This is also partially the player's fault for making a fighter with low CON / not taking Toughness / not investing in hp for favored class bonus.
3) The fighter took focus fire damage from the other pugwampi and thin men. Focus firing on PCs is a realistic tactic for villains, but it also tends to kill the PCs.
4) The GM either multiplied sneak attack on the critical or applied two criticals for both claws when invisibility can only proc one sneak attack. This is a rules mistake on part of the GM.

Even if all of the above is not true, possibility of PC deaths are a part of the game. Even moreso if it's a challenging encounter.

[Steve Danials]

thank you, honestly! I honestly didn't realize that sneak attacks didn't multiply on crits! So, retcon on that...