A rogue's soul is a monster that is found while in the Crucible. One may appear and attack you if you attempt to loot one of the corpses in the Crucible, saying "Who disturbs my slumber?" You must bring it down to low health and direct it back to the corpse in order to be able to loot the corpse. When sufficiently damaged, they would become a Weakened rogue's soul, which hangs its head, doesn't have an attack option and doesn't attack, but will heal itself; if not directed into a corpse it would be ready to fight again in a few seconds. If you take too long to fight one, it would disappear and you would have to loot the corpse again.