When fighting nurgloth the eternal during the Halloween event I and my team discovered that about 3/4ths through the fight his invincible status had become permanent. Just before his 3rd phase where he starts swinging at you with his scythe.
Our comp was: Waystalker, Slayer, Bounty Hunter, and Pyromancer.
The status he has when he is up on his perch suddenly became permanent and we couldn’t damage him.
I am unsure as to what caused it, but it had never happened to me before even though I’ve beaten enchanters lair a few dozen times. I will update if this happens again but I wanted to make it known now as it was incredibly annoying.
I can confirm the presence of this bug, but I think it’s related to the skull from the ritual. As soon as I destroyed it, he switched to the last phase. I don’t know if this is random or not, but it makes kinda impossibile to complete the achievement.
I’ve only tried Veteran and Champion difficulties. On Veteran Nurgloth becomes invincible when he has a third of health remaining. No problem killing him on Champion.
I’ve seen/heard both of those things happen on Legend. For us we got him down to about 1/3 before the man with the skull died, and nurgloth instantly dropped dead. A guy I talked to had the invulnerability problem where they couldn’t damage him down to the final stage until they got rid of the skull manually.
Is the bug character + skull related? I went at him solo on Legend with Zealot and bots Sott (staff build), IB with torpedo, and merc. Went through the whole fight no bugs.
Meanwhile in Cata, he went invincible before phase 2. The group was BW (coru staff), Footknight, Sott (moonbow), and WHC (iirc, our 4th was getting replaced frequently).
It is a rounding issue of health values. The skull buffs enemy HP and it so happens that Nurgloth reaches unfortunate thresholds on Veteran and Cataclysm difficulties which prevent him from fully entering the next/last phase at 33% health. He‘s stuck at .33x HP which is enough to trigger his phasing but not enough to advance it correctly (more or less). Will be fixed.