I'm trying to better understand the Werewolf so that I can design my own varieties of homebrew Werewolves for my campaign. I started by adding together all the stats of the Monster Manual's Werewolf and treating it as if I were building the monster by the DMG's rules.
I used the Hybrid form as the default, since it is the strongest of the three forms in combat.
I calculated the ability scores, AC, and base damage for its attacks. I even doubled its effective HP for the damage immunities it has, as per DMG 277 which indicates that a CR 3 monster with 1-3 immunities should multiply its effective HP by x2.
I discounted shapechanger and its other abilities/effects because they didn't seem to have any impact on challenge. By the time I was done, I calculated the variables and ended up with a CR 1 Monster. (Even though I went with the best-case stats across the board)
A Werewolf is supposed to be a CR 3 Monster. So where are those other two points coming from? The only thing I can think of is its Bite effect (save against lycanthropy) but I was under the impression that saves against non-damage didn't affect CR. What have I not accounted for that is worth two whole points of Challenge Rating? If it is to account for balance, should I account for this 2CR discrepancy in my own homebrew werewolves.
Best Answer
The specific example given by the designers is that the Ogre works out to CR1 by the numbers, but was adjusted up to CR2 because the damage it can do in one attack is more than adequate to insta-kill a level 1 character.
Your Werewolf can do 13 (average) to 20 (max) damage without even critting, enough to be lethal. Certainly this accounts for some upward adjustment.
(A number of commenters have also opined that the x2 adjustment to effective HP may not sufficiently take into account how difficult it is to overcome resistances at low level. See the comment->chat thread below.)
Playtest, though, is the fullest answer. They ran fights with a APL 2 group against werewolves and found it more challenging than other CR2 creatures.