All Characters and Levels
At the main menu enter Y,B,X,Y, DOWN, RIGHT, UP, LEFT, L, L ,RIGHT, RIGHT, DOWN, UP, R, X, LEFT, B, B, DOWN.
All Levels
At the main menu press B, Y, X, B, L, X, R, L, X, R, B.
Complete all current objectives
Pause the game play in story mode,then press X, X, B, X, X, Y, X, X, L, R if done correctly when you unpause the game, a screen will pop up that you have completed all objectives. The rest of the time you have in the level is basically free skate.
