Each time you beat them in a particular outfit unlocks 1 more finale for that outfit.  So on the second victory you will see the first finale, and on the third victory you will see the second finale, etc.

Notes:

• Nobody has more than 1 finale (yet).
• Reloading a saved game and beating it a second time will not count towards your stats or unlocking more finales.
• The duo finales also require the other player to be in the game.

On more thing: you can keep your stats and saved games going between different versions of the game by copying that "saves" folder over into the new version.