He's not that bad to kill. First time we tried it was with me (54 SK) as main tank, but I obviously didn't live long. others in group were all 65 including shaman and others, but no true cleric. We went back and retried him after adding a 65 warrior, 64 cleric, and a 63 SK and took him, although cleric was getting really close to running out of mana. Overall I guess you'd have to say that we had a group of about 8 or 9 mostly 65 level people to take him.
Although he is a spellcaster, he mostly just tanks. It's really awesome to watch him change shape every now and then though. Just suddenly he's something new that he wasn't. :)
I got lucky on the rolls and got this bad boy, so I'm pretty happy. :)