Greater Chosen Arcanists, you can face three or four of these in a room.
They can cast; I think a cone of acid that does roughly 30 damage about two or three times in a row. Even with some good buffs up, it'll eat through them and still probably kill you when you get hit by three or four at once.
I'm not sure what exactly is helpful to balance this a little, turn down the number of castings of this spell, try to ensure fewer spawns of the Arcanists, or what...but I think some balancing is in issue.
The other thing, in the room with a large bridge, it can spawn perhaps upwards of 30 zombies. This isn't necessarily TOO many to beat, but 30+ monsters of any kind causes so much lag it can kill.
These suggestions come after a run through this quest, that Metropakt watched in which everyone except me died twice. So I am coming from what is likely a jaded angle and would love to hear his 2 cents on what he saw or others in the quest.
The rewards are GREAT and the quest is meant for 5th to 11th level. So its possible had we had a higher level party and a better skilled priest (we only had one druid to heal and he ran off half way through after dying once) we may have done better. But I'm thinking even with a GREAT priest, the Greater Arcanists would still be laying people so that is my major concern on balance.