Chernabog? XD Wow, if that's case, give a aero a try and then try to attack him from
behind with your keyblade or something like that, that's what I remember doing with him.
And if not Chernabog, can you at least tell us who's the villian otherwise, we're
assuming its Ansem or Darkside. If it's Darkside, that's simple, just do what you did when
your first on the islands, you know dodge and attack at the right moment when his head
goes down *trying to remember* goes down or whatever, hit him! There I gave you
more then one tip you needed.
I think I went overboard though, didn't I? XD