There isn't much to do roxas... just cast hastega on your party, shell/protect, Magic Break if its not inmune to it... It is not THAT a challenge compairing to the ultimate opcional bosses of FFX. Anyway, my advise is to summon an aeon just before its big attack so the aeon acts like a sponge damage, so the aeon gets killed and you have a lot of turns left to act, thanks to hastega. Try yo lvl up in Omega Ruins also. Good luck
