Godslayer Crown is a Unique Helm in Diablo IV Season 15 for All classes. It drops from Andariel (Echo of Andariel).
Unique power
When you attempt to Incapacitate an enemy, you mark them and all surrounding enemies, pulling them in and dealing [7.5 - 10]%[x] increased damage to them.
Affixes
Primary Core Stat
Armor
Where it drops
General Unique Pool
Andariel (Lair Boss)
Andariel (Greater Lair Boss, 1x Greater Lair Key) - dedicated multi-class Unique
General Unique Pool - every Lair Boss (Initiate, Greater, Exalted, Belial) can drop it in addition to their dedicated table (one guide's Boss Loot Table Cheat Sheet)