Hold L2 and press Up(2), Down(6), Up(3) at the start screen. A volleyball will go from right to left, and splash on the sea to confirm correct code entry. All of the bonus tournament modes are now unlocked.
Bonus characters
Hold L1 and press Up(4), Down(3), Up(5) at the start screen. A volleyball will go from left to right, and splash on the sea to confirm correct code entry. Rocky, Superfrog and Fletcher are now unlocked.