This is the deck I built to fight Marluxia in the end-game. It worked quite well.
21x Any Attack Cards with Value of exactly 3
6x Any Attack Cards with Value of 0
3x Cure Cards with value of 6 or higher
3x Hi-Potions with value of 6 or higher
This deck revolves around the Ragnarok sleight, so you have to be at Level 52 to use it. For bosses, pop Jafar first - for normal enemies, use Marluxia first. This is because bosses can break Ragnarok with 0s and sleights, normal enemies can't. Jafar stops your sleights from breaking, while Marluxia doubles your pleasure and your sleights. So Jafar is better suited for bosses, while Marluxia for normal battles. Sleight Xigbar in once either of those two is done to boost your damage.
Either way, once the right enemy card is in, start sleighting in cards and unleashing Ragnarok over and over again, devastating enemies. Eventually you'll run out of cards, so sleight together a Cure and a Hi-Potion, along with any friend cards you may have gotten. With your stock restored, start firing off Ragnaroks again. With 3 Cures and 3 Hi-Potions, you can fire off plenty of Ragnaroks to quickly crush any enemy party you face. Just keep tapping Triangle, stocking cards and firing your sleights.
Bosses are trickier. If you see a boss start to stock cards for a sleight, let them use it, then bust out a 0 card to halt the sleight and clear the way for your own. Also, the end-game bosses can survive the bombardment of Ragnaroks you'll fire, but with 3 Hi-Potions and Marluxia, if my math is right, that's about 30 Ragnarok sleights you can use before you have to manually reload. When you reload, you should have 14 cards, which is 4 more Ragnaroks. Overall, bosses may survive your 3 Hi-Potion uses, but can still be slain easily. Riku helps against bosses more than normal enemies, helping you retain cards once you've used up your Hi-Potions.
As I said, this deck absolutely crushed Marluxia in the final two battles, and did good against normal enemies, but I'm not sure about other bosses. Still, it's very effective against the final boss, feel free to try it out!