Unlock Mallora board:
Hold L1 + R1 and press X, X, Right, Circle, Circle, Down, Triangle, Triangle, Left, Square(2), Up, at the title screen. Then, release L1 + R1. And select Elise.
Unlock Mix Master Mike:
Hold L1 + R1 and press X, X, Right, X, X, Down, X, X, Left, X, X, Up, at the title screen. Now choose any boarder at the character selection screen.
Unlock Sticky board:
Hold L1 + R1 and press Square, Square, Right, Triangle, Triangle, Down, Circle, Circle, Left, X, X, Up, at the title screen. Then, release L1 + R1.