@PhoenixxFire: The Demicreation should not be broken, but he will indeed heal an absurd amount of damage every few rounds--this is a mechanic. There are ways to control this, but I will not say anything further unless you ask, since I do not want to spoil the fight for you.

Guys we tried everything - collecting the plans, doing things with altar, using decaying touch on the boss, but he just spawns zombies and heals no matter what. We even managed to kill twice the 8 zombie wave, yet still he heals and spawns more.

What is the mechanic behind this, anybody can help? I dont mind the spoiler since we are getting frustrated being stuck here for days.