From the small fraction of the time I stayed alive.
Con: This creature would take considerable effort to defeat!
Hits in the 40k range.
Casts <Balance of the Nameless> frequently on himself and others.
Casts <Samson's Charm>. This spell ignores Divine Aura type effects.
Casts <Invisibility 10>. This despawns him for around 6 seconds.
Generally he fights for a bit, casts a charm on somebody, and despawns (the invisibility 10) for ~6 seconds. Pets don't lose target while he is gone, but players do.
We beat him with a pet heavy group, though clearing around him was so time consuming I can't recommend it. Also, while his minions were around, we tended to get summoned out into the middle of his room, which would usually end badly. Once they were all clear this didn't seem to happen, but possibly because were were fighting in his preferred spot by then.