Invisible and unkillable monsters in map that one shot!!

Non killable non targetable invisible and doing high damage. Had a pack of blue monsters in my map that can one shot a very well geared endgame level 100 character cant even loot after the map they just follow me around extremely fast and shoot one shot balls of fire. They are also in my Mirage and move as fast as a Mageblood char with full move speed flasks