Go to the character select screen and HOLD L1 + L2 + R1 + R2. After that, put in a code below while holding the previous buttons:
Get All Levels: Triangle, X, Square, Circle
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
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
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