Downforce

Go to the main menu and press the following button combinations:

Unlock Invincibility
L1, Triangle, R1, Triangle, Down, Down, Circle.

Unlock Crash arena
Left, Right, Right, Square, Down, Triangle, Triangle,Square.

Unlock Crash arena in 2 player mode
Right, Left. Left, Circle, Up, Triangle, Triangle, Square.

Unlock Beginner trophy
Right, Right, L1, Triangle, Triangle, R1, Right.

Unlock Intermediate trophy
Right, Right, Square, Left, L1, R1, Square, Square.

Unlock Expert trophy
Right, Right, Circle, Left, L1, Circle, R1, Circle.

Unlock Intermediate championship
Down, Square, Up, Square, Right, Right, Left.

Unlock Expert championship
Down, Circle, Up, Down, Circle, Circle, R1, L1.

Unlock Expert AI
Triangle, Right, Left, Square, Up, Circle, Down, Right.