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.