I had my three main fighters get their ultimate weapons and go all around the sphere grid (Tidus, Rikku, Yuna). But that was my second playthrough, just to see if I could do it. My first one was harder, but I never died. Seymour 3 (I think it's flux) wasn't bad, once you learned his telltale moves. Besides, I had Rikku mix me up an electro marble with a petrify grenade and poisoned him, doing 1500 damage every turn.