Several Characters (mostly Luffy's crew; wich consist of Luffy, Zorro, Sanji, Ussop, Chopper, Nami and Nico Robin) have 3rd and 4th Alternate costumes which are unlocked by doing several tasks.

Luffy's Crew 3rd alternate costume
In training mode, complete the training list with Luffy , Zorro, Sanji, Ussop, Chopper, Nami and Nico Robin.

Luffy's Crew 4th alternate costume
To do this, you must choose the VS option, go against computer in Hard with 3 rounds and try to finish all the rounds with the super level 2 special.

Wiper's 3rd Costume
After getting all the costume, complete Training mode with Wiper again.

Shanks 3rd and 4th Costume
After getting Luffy's pirate 3rd & 4th costume, complete Training mode with Shanks.