to defeat him simply get the knights of the round materia(you must have a gold chocobo) and cast knights of round and he will die

ok SAFER SEPHIROTH is a little harder you must be aware of pale horse and super nova, after he uses these be prepared for healing....equip pheniox and final attack materia and link these two so when the person that has this is on dies will resotre all party members HP and attack the eneime.also use ominslash and everyones final limit breaks. YES use knights of the round and bahumat zero. ALSO THIS IS A MUST HAVE have the resore materia up to cure 3 and link that with a ALL materia and that way u can cast regan on your party and use cure 3.... and this should make it easier to kill sephiroth