Easy Way to Beat Bosses
Take a deck stocked almost completely with zeroes! Include like 5 nine cards at the beginning, as well as some heal cards (zeroes) at the end. Shuffle past your nine cards to your zeroes. Now, don't ever attack your foe, simply break every attack they try to use on you! Then, once they have to reload (which will happen more and more frequently as you consistently break their combos, wasting their deck), attack all out! Here's where I switch back to my nines, too, especially if you don't have enough 0 cards or if you want to use combos. Anyway, once they're done reloading take the defensive again, repeat as necessary (it will probably take a while...), and ta-da! Easy win!
I used this method against Captain Hook and Marluxia with much success.
More tricks, tips and cheats for this game are right here - Kingdom Hearts: Chain of Memories cheats
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