i have only just beat him myself because i started a new game not long ago. heres some advice. use bio, it will poison him and do about 200 damage per poison damage. use life as soon as someone dies, have cure and all on so you can cure all (obviously). and i dont think i have any more advice. i personally beat him with level 27 cloud, level cant remember aeris and level 28 red xiii, at the end of the battle cloud and aeris were dead and red had about 200 health left.

i hope this helps