Capture at least 2 Splashers, 2 Achelous, and 2 Maelspikes from
the flooded part of Mt. Gagazet Cavern. IF that doesn't work then cature 5 of every monster and that will unlock him. If you want to defeat him then make sure that at least Wakka and Tidus can hurt more than 65,000 damage with phy. attachs.