This dude took about 15 tries before I realised the main thing stopping me from killing him was the accuracy debuff
Eder - full deflection tank, away from main party, lots of endurance potions.
need: massive buffs to accuracy and immunity to paralysis and stun (thanks Durance you crazy old coot)
Get Eder to attack an ice blight and turn off his AI. keep him alive as long as possible (armor with 2nd chance can help).
DO NOT ATTACK THE DRAGON
kill off as many stray ice blights and oozes as possible without getting too close to the dragon (their damage is not that important)