Hidden Characters:
Unlock the characters. 
Certain characters can only be unlocked after reaching a certain requirement. 

Play as Orm:
Successfully complete Event Battle as Chopper.

Play as Smoker:
Successfully complete Event Battle as Zoro.

Play as Wiper:
Successfully complete Event Battle as Luffy.

Play as Enel:
Unlock Smoker, Crocodile, Wiper, and Orm, then successfully complete Event Battle as Luffy or Wiper.

Play as Hina:
Unlock Enel, then successfully complete Event Battle as Usopp under the hard difficulty setting.

Play as Bon Clay:
Unlock Hina, then successfully complete Event Battle as Sanji under the hard difficulty setting.

Play as Ace:
Unlock Bon Clay and the third costumes for Luffy, Zorro, Nami, Usopp, Sanji, Chopper and Robin (by completing training mode with them), then successfully complete Event Battle as Smoker under the hard difficulty setting.

Play as Shanks:
Unlock Ace, complete Event Battle under the hard difficulty setting as Luffy, Zorro, Nami, Usopp, Sanji, Chopper and Robin, and unlock the Windmill Village and Marine HQ stages. Then, successfully complete Event Battle as Luffy under the hard difficulty setting.

Alternate costumes:
Complete the following goals to unlock the corresponding costume for the indicated character.

Luffy's group's third costume: Successfully complete training mode as Luffy, Zorro, Nami, Usopp, Sanji, Chopper and Robin.

Luffy's group's fourth costume: Win Grand Battle (three rounds, hard difficulty, unlimited time) with Luffy's group's third costume against any CPU player. Note: You must win all three rounds with a level 2 special.

Shanks' third and fourth costumes: Unlock Luffy's third and fourth costumes, then successfully complete training mode as Shanks.

Wiper's third costume: Unlock Luffy's and Shanks' third and fourth costumes, then successfully complete training mode as Wiper.

Alternate commentary:
Successfully complete Event Battle under the normal difficulty setting as any character to unlock that person's voice as a commentator.

Super Hard difficulty:
Successfully clear all moves for all sixteen characters in training mode.