That's because he is a cleric....Wrath is a cleric spell... He does not Complete heal, but begins healing himself around 40% health. I was soloing the entrance (green/Light blue) at 55 with my druid. Use Winged Death, thorns and melee him up close, when he gets to 60% use Scoriae, he will heal, but hit him continiously with Scoraie...it does more damage than his heal, once under 20% he will start running (snare em) and he will stop attacking.