I seem to be completely stuck on this quest, and I have no idea what I'm supposed to do.

Immediately after using Comet, Faunehm will cast Chaotic Verse, giving you a debuff called Enamation that reduces your damage done and increases your damage taken. This causes Faunehm to deal more than double his normal damage against you, with his melee hits hitting for over 3000 damage and his Dark Star ability hitting for more than 8000! Combined with your reduced damage, this essentially makes Faunehm unbeatable.

Is there anything I'm missing here? I've tried every option I could think of, but nothing seems to work. Standing at a distance doesn't work, standing in melee range doesn't work, stunning doesn't work, using Diversion to keep the aggro on Estinien doesn't work, tanking the Comet ability doesn't work, and standing still and letting the dragon hit me while Estinien supposedly uses some ability doesn't work either. How am I supposed to beat him like this?