Mordrath

Mordrath,  Gate Defense Captain is a Super Unique Executioner found in The Ram during the Breaching the Fortress quest in Diablo III.

He has Extra Health affix, but his true power is spawning more Chained Hooks as long as he lives, making it impossible to free the ram for the final blow before Mordrath is killed. In addition, he attacks simultaneously with endless Ghastly Seraphs and Winged Assassins, and does so in a very limited space, so glass-cannon players may find it very challenging to endure the whole fight.

In addition, the fight is instanced: should player die, they cannot revive at corpse, and will need to start all over again.