The final floor consists mainly of a long, thin path guarded by two Behemoths. One is at the start, the other at the end.
Bahamut counts down from 5 before unleashing his MegaFire attack, which is devastating. The key, as mentioned in a book in the Cave of Summons, is to Reflect this attack back at him using Wall. If you fight him with FuSoYa in the party, you'll have two casters who can cast Wall, and you should be able to protect most if not all of the party. Alternately, you can have Characters use any Star Veils and Moon Veils you've found to grant Wall even faster. Once your defenses are in place, go all out in attacking, hoping to win the fight before the Walls wear off. Whatever you do, don't set the battle mode to Active!
Bahamut counts down from 5 before unleashing his MegaFire attack, which is devastating. The key, as mentioned in a book in the Cave of Summons, is to Reflect this attack back at him using Wall. If you fight him with FuSoYa in the party, you'll have two casters who can cast Wall, and you should be able to protect most if not all of the party. Alternately, you can have Characters use any Star Veils and Moon Veils you've found to grant Wall even faster. Once your defenses are in place, go all out in attacking, hoping to win the fight before the Walls wear off. Whatever you do, don't set the battle mode to Active!