You can rape him real good by using reflect on him as an attack (not a shield) if you're in Master Form. I like to equip the Fatal Crest keyblade to Master Form because it has a good magic stat and it's ability is useful here. Drive into Master and then use Reflect on him, he will get caught up and be unable to move. Keep spamming reflect until you run out of MP. While you're doing this he cannot move, the reflect attacks do damage, and then one large burst of reflected energy damages him upon your last use. You then just start attacking him in Master form immediately after that last reflect because Berserk will give you a temporary strength boost, but most importantly, you will be able to perform combos endlessly.