All Straw Hat characters but Vivi start with their 1P and 5P costumes, and in Robin's case the 4P as well. In general, 4P costumes will be found first, while 2P costumes appear later in the game and are more complicated to get. Any costumes unlocked in Adventure mode will be usable in every other mode.

In unlocking Luffy's 2P costume, make sure not to fight Crocodile until after you have travelled to Jaya and are prompted to finish Crocodile before proceeding, or your game will end at the Crocodile fight.

An easy way to beat Ace(Trace) with Chopper in the Graveyard of Ships is to use Chopper's "Health" attack (Jump+O) non-stop. Beware of rolling bombs.