Tiny mode: 
At the main menu, press L, Z, Left, Right, B(2). 

Tag mode: 
At the main menu, press Z, X, Z, X. 

Low gravity: 
At the main menu, press Left, Right, Up, Down, B(3).

Unlimited turbo:
At the main menu, press Down(3), L, R, Z.

Bouncy bike: 
At the main menu, press Up(2), Y(2), X(2).

Big heads: 
At the main menu, press B, X, R, L, Right.


by unknown