I beat this tower at level 30-35. I'm only on level 40 in Kefka's tower. I had Ultima and Reraise with both Terra and Celes. Gogo Mimicked everything which was damn useful and Mog just done nothing. They all had Reflect Rings apart from Terra who had Soul of Thamasa and Gold Hairpin for two Ultima's for the price of one. If you haven't got Ultima or Reraise then just run around getting in fights at the Fanatics Tower. You get like 7 AP a fight.