Kingdom Hearts: Chain Of Memories

Unlock Revrese/Rebirth

Simply beat the game as Sora, wait through the credits (and a decent song), and you will be able to play as the REAL Riku.

Fun Card Combos

My personal favorite, combining 3 Clouds. He starts flying in the air and strikes down at random enemies 3 times. Combining 3 Goofy's makes him to a tornado spin that damages enemies. Combining 3 Heals restores health completely (as far as I know). 3 Thunders damages all enemies. There are many combos, try them out for yourself!