Dark Cloud Demon Shaft Elemental Immune Monsters
Ahh, so you've tried every elemental attribute on this guy and you've paused the game and ended up here, aye? Well there's one thing you haven't tried yet, obviously... Turning off ALL elemental attributes and hitting his ass with plain white damage. Once you do that you can quite easily take this guy down.
Oh yeah, later on there are a few more mobs like this!
Heart Floors 60 - 80
Space Gyon Floors 60 - 80