All cheats for this game by platform:
Wii U
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Unlock End Credits Tablet
Beat final boss and speak to cuttlefish.
Unlock Campaign Gear
Beat the Final Boss in the Single Player Campaign in order to unlock the following 2 sets for use in multiplayer (Each consists of a hat, shirt, and shoes).
Unlock Weapon
Upon killing the boss in each set of stages you are awarded a scroll. Take that scroll to the weapon shop to unlock 5 additional weapons.