Pause the game and hold L + R. Now use these passwords:
Unlock levels: Y, X, Y, X(2), B
All moves: Y, X, Y, B(2), X
All mini-games: Y, X, Y(2), B(2)
More HP from food: Y, X, Y, X, B, Y
Extra damage: Y, X, Y, X, Y, B
Always power golf: Y, X, Y, X, B, X
Bonus comic 1: Y, X, B(2), X, Y
Bonus comic 2: Y(2), B, X, B, X