Other people reckon you should go all out DD when he's on the ground since that's the easiest way to hurt him.
When he goes airborne you need to knock him down by damaging him, using well timed spells (can't hit while he's casting or it'll just heal him). Some people seem to report excessive healing of him makes him stay airborne longer, which would correspond with others saying you need to do ~1k damage to get him to land again I suppose.
Culshar Geezer replied
766 weeks ago