Mantle of the Grey is a Unique Chest Armor in Diablo IV Season 15. It comes from Harbinger (Lair Boss drop).
Unique power
Juggernaut Oath makes your Juggernaut Skills 25% larger but Consumes up to 16 Resolve, granting [4.0 - 6.0]%[x] increased Juggernaut Skill damage for each point Consumed.