Pact of Bone is a Unique Ring in Diablo IV Season 15. It comes from Harbinger of Hatred (Lord of Hatred Lair Boss) per one guide; 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
Your Minions gain [30 - 35]% Attack Speed and Critical Strike Chance. When one of your Minions die, your other Minions enrage, dealing [30 - 35]%[x] increased damage for 3 seconds.
Affixes
+5-25% Critical Strike Damage
111 All Resist (inherent)
Where it drops
Harbinger of Hatred (Lord of Hatred Lair Boss) per one guide
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