His mortal enemy? Cataracts.

Arcane: Venom
Base Rarity: Legendary
Troop Type: Undead, Monster
Troop Role: Warrior
Troop Id: Boss_K36 / 6609
Max skills: 18    18    27    14
Kingdom: All-Seeing Eye
Kingdom Id: 3039
Trait #1: Undying
Immune to Poison, Disease, and Death Mark.
Trait #2: Deep Magic
Gain 5 Magic when attacking Delves.
Trait #3: Death Ray
Death Mark the first enemy when I take damage to Life.
Spell: Undying Gaze
Description: Deal [Magic + 3] damage to the first 2 enemies, and transform Yellow Gems to Skulls to boost the damage. [1:1]
Mana Color: Green, Purple
Mana Cost: 15
Spell Id: 7933