PS, don't even bother moving in phase2 of TheBlackKnight. The "Death&Decay" type spell does next to no damage. It's all about timing your Thunderstorm to blow up the adds before he corpse explodes them. If you blow it too early, before your magma's have done enough damage, they will run back and you won't be able to kill them all before he explodes. Only move just before he's about to switch into phase3. Move off the AoE section and chain heal to full, so that you don't have to deal with phase3 damage plus the D&D if it's still on the ground.

I find bloodlust/heroism ChainHeals every 3rd spell in phase3 easily outheals the AoE damage. ShadowResAura knocks 25%-ish off the AoE.