I'm a bit baffled with translating Mokmurian's (from Pathfinder #4) CR to the Pathfinder RPG. In 3.5 I assume the relevant rule is the one for adding nonassociated class levels:
If you add a class level that doesn’t directly play to a creature’s strength the class level is considered nonassociated, and things get a little more complicated. Adding a nonassociated class level to a monster increases its CR by ½ per level until one of its nonassociated class levels equals its original Hit Dice. At that point, each additional level of the same class or a similar one is considered associated and increases the monster’s CR by 1.
Mokmurian is a stone giant (CR 8) with 14 levels in the nonassociated class wizard. According to this rule up to 14 - i.e. all - of his wizard levels should increase the base stone giant CR by ½ ("until class level equals original HD"), meaning his final CR is:
Total CR = 8 + ½ * 14 = 15 (as printed in the adventure)
However, in the Pathfinder RPG the rules are different. Stone Giants are listed as a creature with a combat role in Appendix 13 of the Bestiary, thus wizard is not a class marked "key" in Table 2-4 in Appendix 2. The rule reads:
While adding a class level to a monster that stacks with its existing abilities and role generally adds 1 to its CR for each level taken, adding classes that do not stack is more complicated. Table 2–4 gives general guidelines regarding which core classes add directly to a monster’s abilities based on its role. Classes that are marked “key” generally add 1 to a creature’s CR for each level added. 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). Creatures that fall into multiple roles treat a class as key if either of its roles treat the class as key. Note that levels in NPC classes are never considered key.
Now this means that only the first eight of Mokmurian's wizard levels are counted half ("until the number of levels equals or exceeds the original CR"), his six remaining wizard levels are treated as "key" levels. This way, his total CR can be calculated as:
Total CR = 8 + (½ * 8) + 6 = 18
Thus, measured according to the rules of the Pathfinder RPG, he would really seem a very challenging opponent for a level 11-12 party.
Or am I making a mistake here?
If ran right he should be a very challenging opponent for the PCs
Mokmurian TPK'd my level 11 gestalt party. He was the only TPK in the entire adventure path. He's absolutely a higher "effective" CR than 15, although I don't think he was truly a CR 18 either. I believe I pegged him at 16 or 17 for experience purposes, but it was a long time ago and I don't remember for sure.
He's one of the most challenging encounters in the entire series because he's so formidable in his own right, he has good tactics set up, and he's had at least one chance to watch the PCs fight and learn their tactics. He can even hold his own in melee well enough that he can get away with isolating himself with a full BAB character (with a solid fog, wall of force, or whatever else) and kill that character, which happened in my game.
PS: His fogcutting lenses are practically cheating. If your PCs are anything like mine, they'll howl at being blasted to bits while within a solid fog. Although solid fog is significantly weaker in Pathfinder than it was in 3.5.
When I converted him I knocked off a couple wizard levels to bring him back down to CR 15. I don't mind throwing a challenging fight at my players, but I don't think I want an encounter that's even more deadly than the one with Xanesha. Of course, if the characters have become really powerful, and the players are getting a little too full of themselves, I may add the levels back in and give them a really good smack-down :)
in my group, a level 11 1/2 orc cleric of gorum beat him one on one.
my wizard 7/ loremaster 3 (at the time) (now a wizard 7 loremaster 6) the hill dwarf fighter 11 and the high elf monk 11, basically sat and watched the show. preparing to leave, should things turn ugly. it was a challenge the cleric self imposed, where he won in 3 rounds.
but the 11th level party cleric himself was more like a CR 18. if you count the fact, he prebuffed himself before the fight. and had a few scrolls of heal that he didn't need. he was barely even nicked. it was in effect, similar to a 1 turn blitz. now thats a reason to be careful about allowing an accountant (or one of a similar number crunching proffession) at your gaming table.
Speaking of CR's I think the one for the Black Monk is kinda high... We stumbled across that secret door and my wizard dropped a torch down. So we see this strange being flitting back and forth illuminated by the flame. I shot it with Disintegrate, it died, because undead have incredibly low Fortitude saves. Our DM was frothing because it was supposed to be such a cool encounter.
My party took him and his honor guard with only one casualty, but with something like three to five instances of party members dropping to negatives and getting pulled back out by the cleric. It was a hard fight, but not unwinnable for them.
The stand-out moment for me was actually not the direct Mokmurian combat, but instead when his guardian stone giant snatched up the group sorcerer and began to use him as a club to whale on the rest of the party.