Beat Crocodile in Luffy's adventure mode to unlock Buggy and Mr. 0 Crocodile's adventure mode, continue with Luffy's adventure and defeat Eneru to unlock Chaser's adventure mode.
Effect - Code
Chaser - In Chaser's adventure mode, get Chaser to Lv. 15 and use him once in battle.
Eneru - In Mr. 0 Crocodile's adventure mode, use him once in battle after he joins the crew.
Hawk-Eyes Mihawk - In Chaser's adventure mode, use him once in battle after he joins the crew.
Kuina - In Chaser's adventure mode, get Kuina to Lv. 15 and use her once in battle.
Mr. 2 Bon Clay - In Mr. 0 Crocodile's adventure mode, use him once in battle after he joins the crew.
Nico Robin - In Luffy's adventure mode, use her once in battle after she joins the crew.
Ohm - In Mr. 0 Crocodile's adventure mode, use him once in battle after he joins the crew.
Portgaz D. Trace - In Buggy's adventure mode, use him once in battle after he joins the crew.
Red-Haired Shanks - In Buggy's adventure mode, use him once in battle after he joins the crew.
Support Characters - In adventure mode, use a support character in 3 battles, then they can be used by any character in Grand Battle mode.
Zeff - In Chaser's adventure mode, get Zeff to Lv. 15 and use him once in battle.
Unlocking Extra Costumes- Straw Hat Pirates
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.
Effect - Code
Chopper 2P - Obtain the bonus item "Santa Hat" by beating Ace(Trace) with Chopper at a Wrecked Ship in the Graveyard of Ships
Chopper 4P - Obtain the bonus item "Panda T-shirt" by beating Nico Robin with Chopper at Erumalu in Alabasta Kingdom Sea area
Luffy 2P - Obtain the bonus item "Pirate Coat" by beating Crocodile the first time at Alubarna in the Alabasta Kingdom Sea area with a super attack
Luffy 4P - Obtain the bonus item "Cool Shades" by beating Buggy with an item at Orange Village in the Orange Village Sea area
Nami 2P - Obtain the bonus item "Yellow T-shirt" by beating Buggy at Vermillion Town in Jaya Sea Area with Nami
Nami 4P - Obtain the bonus item "Fashionable Sunglasses" by beating Chaser at Navy Base No.64 in the Inshore Alabasta Kingdom area
Robin 2P - Obtain the bonus item "White Hat" by beating Ohm the first time at the Ruins in Skypiea
Sani 2P - Obtain the bonus item "Gaudy Shirt" by beating Don Krieg at Vinegar Village in the Jaya Sea area with Sanji
Sanji 4P - Obtain the bonus item "Necklace" by beating Chopper at Big Horn in the Drum Kingdom Sea area with Sanji
Usopp 2P - Obtain the bonus item "White Bandana" by beating Kuro at Mock Town in the Jaya Sea area
Usopp 4P - Obtain the bonus item "Sunglasses" by beating Nami at Coco Village without knocking her out
Zolo 2P - Obtain the bonus item "Goggles" by beating Arlong at Spice Village in the Jaya Sea area
Zolo 4P - Obtain the bonus item "Necklace" by staying alive for 30 counts against Hawk-eye Mihawk at Blue Town in the Syrup Village Sea area