Armorer's Bane, Harrower of Filth, is a Unique Scavenger found in the Watch Tower Level 2 in Act I of Diablo III. He spawns for the Scavenged Scabbard event.
Initially, he does not attack, but attempting to retrieve the scabbard or hitting either member of his pack causes him to retaliate. Killing it is not even required for the event.
In combat, he has Knockback and Fast affixes.