Encountered an un-killable Bug Swarm type mob, the type that looks like a bunch of flies. Playing on a wizard level 60 normal rift. Shifting Deception Level 3, it was a graveyard tile set. The mob was part of rare group, the blue type that have abilities. At one point it flew over an iron fence and the name disappeared. It continued to chase after me and could attack me, preventing me from teleporting back to town, but I couldn’t damage it at all. I was using a Sebor’s Nightmare Belt and it might have died form a haunt while it was flying over the fence, but I can’t be sure.