Actually Mirage Tower is only 50 floors, my brothers and I beat it with a party of Acolyte (me) Blacksmith and Dark Knight
Blacksmith is best dps in the game imo and Dark Knight is just w/e average class
and Acolyte sucks... I have trouble in the story line cuz I can't deal damage and my AI teammates end up dying.
You're better off getting Soma Bringer `-` this game doesn't really offer much in terms of multiplayer