At the 'Title' screen hold L1 + R1 and enter the following codes to unlock the corresponding effect. If the code has been entered correctly you will hear a confirmation sound.
Unlock Cheat Mode:
Press X, Triangle, Right, Circle, Square, Down, Triangle, Square, Left, Circle, X, Up.
All Boarders have Full Stat Points:
Press Triangle(2), Right, Triangle(2), Down, X(2), Left, X(2), Up.
Unlock Sticky Boards:
Press Square(2), Right, Triangle(2), Down, Circle(2), Left, X(2), Up.
Unlock Mallora Board:
Press X(2), Right, Circle(2), Down, Triangle(2), Left, Square(2), Up. Select Elise and start a course and she will have the Mallora Board and a blue outfit.
Unlock Mix Master Mike:
Press X(2), Right, X(2), Down, X(2), Left, X(2), Up. Select any boarder at the 'Character' selection screen and they will be replaced by Mix Master Mike on the course with the ubers of the character that was originally selected.