Blood-Mad Idol is a Unique Amulet in Diablo IV Season 15 for All classes. It comes from General Unique Pool; 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).
Unique power
You are always Berserking but take 200%[x] increased damage as Burning over 8 seconds. While Burning, Berserking grants an additional [80 - 100]%[x] increased damage.
Affixes
Primary Core Stat
Attack Speed
Where it drops
General Unique Pool
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)