Will of Rathma is a Unique Amulet in Diablo IV Season 15. It comes from Random world drop / any Lair Boss (one guide: 'drops at any Difficulty Tier, increased drop rate per Torment tier'); 3.2.1: all Uniques drop from level 1 in any Difficulty; targetable via Horadric Cube reroll.
Unique power
Vulnerable, Weakened, Crowd Controlled, or Corrupted enemies are Afflicted, taking 60%[x] increased damage from you (3.2.1: increased from 40%[x]). Curse Skills deal [600 - 750] Shadow damage when applied to Afflicted enemies.
Affixes
+8-28% Vulnerable Damage
Where it drops
Random world drop / any Lair Boss (one guide: 'drops at any Difficulty Tier, increased drop rate per Torment tier'); 3.2.1: all Uniques drop from level 1 in any Difficulty; targetable via Horadric Cube reroll