Bring Null Damage Wall Monsters
The main gimmick is damage walls. Bring at least 3 NDW monsters to avoid any damage.
Bring a Lot of Damaging Bump and SS
Bahamut X has a lot of HP. You need a lot of DPS bump combos like Rebound Laser, One-Way Laser and Plasma to take him down. Some good SS are Meteor, Command or SS with Slayers.