Okay for about a couple years I known this that Sephiroth has a weakness in his ultimate attack during the fight in KH2. Well as he does Heartless Angel (the move where Sephiroth takes all your Hp, all but 1, your Mana and leaves you with squat.), you have a split second to use Curaga or Cura (which ever is in your disposal at the time.) on yourself, before he takes your mana. This little helping glitch helped me through that battle a couple of times. And I hope it helps you