Invulnerable Rare

While in a Mirage portal, one of the rare mobs stopped moving for ~10 seconds and was immune to damage. It eventually cast a spell and moved again, at which point it could be damaged and was slain. This occurred in the Mirage zone spawned in the Crematorium, and the mob was a rare version of the Ash Prophet. The bug reference number is 4,114,014,919.