Erra, Breaker of the Silver City, is a Unique Mallet Lord found in the Gardens of Hope Second Tier in Act IV of Diablo III, added in Patch 2.2.0. He may be nominated a bounty target.
In combat, he gains Arcane Enchanted, Vortex and Missile Dampening affixes. He also deals increased damage, but moves incredibly slowly.
A bounty may be offered to kill Erra, in which case the secondary objective is to kill 50 enemies.