Finally managed to get "Watch him die" tonight, on 5th attempt.

didn't kite, didn't kill group by group, just went full zerg. Used a cleansing totem
use a scroll of agility, a 2min armor pot (waited on cooldown before fight), a health pot, and 40stam food
- shield thrown on left group, taunt on boss, consecration, aoe stun
- start focus fire on boss
- start burst tools: mirror image, starfall, treants, bloodlust (Not Fire Elem!), pop dodge trinket
- hand of protection on priest, shield (-50% dmg) on tank
- drop Earth Elem (gives 3-5 seconds respite)
- priest spams Holy nova.

a couple tries before i wipes with the boss at 83hp. >.< yes, one tick of consecration would have killed it
he seems to get some massive damage reduction around 1%hp, the last 10k were as long as the previous 40k hp it seemed.