If you beat the Arcade Mode with Maka, Black Star and Death The Kid, they will unlock new Clothes and new colors. The others characters only will unlock new colors.
Unlock Excalibur
Beat the Mission 51.
Unlock Free
Beat the Arcade Mode.
Unlock Medusa
Beat Maka's Adventure Mode.
Unlock Ox
Beat the Arcade Mode.
Unlock Shinigami
Beat the Arcade with ALL Characters and the Adventure once.