Downforce

Get invincibility:
Go to the main menu and press L1, Triangle, R1, Triangle, Down, Down, Circle

Get Crash Arena:
Go to the main menu and press Left, Right, Right, Square, Down, Triangle, Triangle, Square

Get Crash Arena 2 Player:
Go to the main menu and press Right, Left, Left, Circle, Up, Triangle, Triangle, Square

Get Advanced Enemy AI:
Go to the main menu and press Triangle, Right, Left, Square, Up, Circle, Down, Right

Get Beginner Trophy:
Go to the main menu and press Right, Right, L1, Triangle, Triangle, R1, Right

Get Intermediate trophy:
Go to the main menu and press Right, Right, Square, Left, L1, R1, Square, Square

Get Expert Trophy:
Go to the main menu and press Right, Right, Circle, Left, L1, Circle, R1, Circle

Get Championship Intermediate:
Go to the main menu and press Down, Square, Up, Square, Right, Right, Left

Get Championship Expert:
Go to the main menu and press Down, Circle, Up, Down, Circle, Circle, R1, L1