Behemoth:
Like TrapDoor, it�s not really a boss, but it�s still tough. Throw Excaliburs if you duplicated them, or attack with Edge, Have FuSoYa heal, summon with Rydia, have Rosa Heal and Cecil attack. Keep healed and you may want to Berserk Cecil.
Enter the next room, and as you go across the bridge, another Behemoth fight. As you near the end of the bridge, you have the third and final Behemoth fight.. When won, heal and use a couple of Ethers on Rosa and FuSoYa. Head up and talk to the man. You will fight.
Bahamut:
There is a very good reason why you came here now. Not so you could get some good levelling, but because you have FuSoYa. At the beginning of the battle, use the Wall spell on everyone you can in this order: Rosa, FuSoYa, Rydia, Cecil, Edge. Use StarVeil or MoonVeil on some characters if necessary. Bahamut will count down from 5, then use MegaFlare. The reson we used Wall is so that the attack would bounce back and hit him. Have Edge Throw, Cecil attack, Rydia summon Leviatan. You should win OK.
Once you win, Rydia will learn Bahamut. Leave, using Exit or Warp, depending on who�s alive. Return to the Lunar Whale, and head back to Earth.