Go to the character select screen and HOLD L1 + L2 + R1 + R2 and then put in a code below while holding these buttons

Get All Levels: Triangle, X, Square, Circle

All Skaters: Circle, Triangle, X, Square

All Boards: X, Triangle, Circle, Square

Bart with Big Head: X, Square, Circle, Triangle

Frink with Big Head: Square, X, Triangle, Circle

Lisa with Big Head: Square, Triangle, X, Circle

Frink Cool: X, Circle, Triangle, Square

Krusty Businessman: Circle, Triangle, Square, X

Otto in Shades: Square, X, Circle, Triangle

Wiggum Big Head: X, Circle, Square, Triangle

Wiggum Man Eater: Triangle, Circle, Square, X

Get $99: Triangle, X, Circle, Square

Get Fuzzy Skaters: X, Triangle, Square, Circle

Marge a Demon: X, Square, Triangle, Circle

Lisa Gangster: Square, Triangle, Circle, X

Bart a Gangster: Circle, X, Square, Triangle

Nelson Big head: Triangle, Square, Circle, X

Homer Big Head: Circle, X, Triangle, Square

Nelson a Ballerina: Triangle, Square, X, Circle

Homer in Tights: Triangle, Circle, X, Square