They can be a high level, I know. Last night with my 15 ENC I encountered some, and I remember one that I was taking. I casted 2 chokes and 1 chaotic feedback, and he resisted them all. I had to tashan before I could get a damage spell to stick.
his magic didn't seem that powerful to me. On my way back to Qeynos to freeport, he frost rifted me while before the camping group could get him, and it only dealt like 20 damage. I would think it's be higher