Go to the Omega Ruins, and level up for an hour or so. Also, make sure that you have the weapon for Tidus with the Double AP ability (!!!). You can get to it with the airship. You will gain atleast a level per fight in the Omega Ruins easy, and will get about 5 per guy in the last fight. It's awesome. Do that, and get Anim, and you'll have no problem beating the last boss.
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