Random Thought: Troll Elder Matron CR

[DwarfInTheFlask]

Ok so looking through the unofficial Pathfinder SRD I noticed something odd.
The Troll Elder Matron has a CR of 10, she is a 10th level Witch.
The Troll Monarch is a CR 15 and is 10 levels a Warrior.

Average Troll has a CR of 5... so why is the Matron's CR so low?
I mean she is a full 10 levels of a spell caster, casting two Level 5 spells. Seems to have a fairly good amount of feats, especially since it seems like she specializes in fire.

[Forrestfire]

CR is overall a very broken system, particularly with respects to advancing class-leveled monsters (see the very bottom (http://paizo.com/pathfinderRPG/prd/bestiary/monsterAdvancement.html)).

Because trolls are a "combat"-role monster, not a "spell"-role monster, adding spellcaster levels by these guidelines increases CR by 1 per 2 class levels added, while adding warrior-type class levels adds CR at a 1:1 rate. This, as you've noticed, leads to some very silly situations.

Personally, I'd peg a level 10 troll witch at around CR 12-13; the troll abilities don't add a whole lot to their ability to cast, but they're still meaningful as far as durability and potentially damage go.

[DwarfInTheFlask]

Ah, Thank You. I was just so confused. But yeah I would rate is more CR 13 or so because a 200 HP witch is insane at level 10. I mean human witch rolling 4s for HP with a Con bonus of +2 only has 71 HP. The fact she regenerates 5 points a round means she is a tough one to crack. Sure she has an AC of 18 but she is a battle witch at that point.

And as a part-time DM I was thinking of what I would do with one of these in a game and I could easily see with a change in the Hex turning this in a TPK.

[bahamut920]

Perhaps a more accurate estimation of CR is to go with 1/2 CR for NPC class levels, full CR for PC class levels, and only use 1/2 of the monster's base CR if the PC class goes against its intended role? It seems like that would work for our troll matron here, at least - 10 Witch levels is CR +10, but the fact that spellcaster levels are "non-associated" with the Troll base means only 2.5 of the troll's 5 CR is the "base", meaning a CR in between 12 and 13. Whereas the troll monarch would only be getting +5 CR from its NPC Warrior levels but would get all of its 5 base troll CR for a CR of 10 total.

[zlefin]

also, a lot of people get the rules wrong, and miss a key part of them:
"Classes marked with a “—” increase a creature’s CR by 1 for every 2 class levels added until the number of levels added are equal to (or exceed) the creature’s original CR, at which point they are treated as “key” levels (adding 1 to the creature’s CR for each level added). "

they're often forgetting that clause (3.5 has a similar clause using Hit Dice instead of CR)

so after 5 levels of witch it should start counting as a key level and add 1 cr per level