Okay, you has to be at least about level 40. You need to have the guard ability equipped before you fight him so you can deflect his attacks. Other then that just use the reaction commands, attack him, dodge if you need to and heal when you need to. :) Oh, and you probably shouldn't use your drive forms cuz you're most likely to turn into anti-form instead of what you actually want. Hope this helps :) Good luck!
Well, be sure to have LOTS OF POTIONS. Your MP will run out very fast from spamming cura >_>
But, you NEED the guard ability to deflect.
When the battle starts, spam triangle and the X. and be prepared to drop everything and run. its OKAY if donald and goofy die. they dont really do much anyway.
Also, when he does that thing where the platform is just a square, dodging and deflecting is of the utmost importance. When the final stage starts, dont heal, dont do anything, just run in a circle around the edges of the square. It may not sometimes, but if you just run around, you should be able to dodge them. If not...then be prepared for some epic death X_X