He puts a disease dot (Corrupting Seed) on different group members - this must be cured as it hits for roughly 1.5K to 3.5K per tick, depending on resists. Nox pots work best since healers must use the break between knocks to heal group.
He does AOE knockback with heat damage (Blastwave) every 12 seconds which interrupts casting, heals, etc. The dmg and knockback can be resisted.
At 20%, burn within 15 sec. otherwise he will full heal (Fel-charged Overload).
He also casts a magic-based power drain (Soulsiphon).