Skip ahead to 7:25 to see the special movie. In order to get the special ending you have to: lock all worlds, find all 99 Dalmations and beat the Hades cup at the Coliseum.
From Wikipedia:
is a series of action role-playing games developed and published by Square Enix. It is a collaboration between Square Enix and Disney Interactive Studios, and is under the direction of Tetsuya Nomura, a longtime Square Enix character designer. Learn about Kingdom Hearts
