Slarth the Tunneler, Devourer of Angels is a unique Scavenging Tunneler that can be found in the Battlefields of Eternity in Act V of Diablo III.
It has Frozen, Frozen Pulse and Electrified affixes.
A bounty may be offered to kill Slarth, in which case the secondary objective is to kill 150 enemies.
Sometimes two instances of Slarth the Tunneler can appear in the same game session, presumably due to a bug.