For an easier game, pause and press C, A, Right, B.
Extra Life
Pause the game and press C, A, Down, A, Left, Left, A, C.
Extra Time
For more time, pause the game and press A, C, A, Down. You'll hear a tone if you did this right.
Level Select
Pause the game and press C, Up, B, Right, Up, B, B, A, Down, Up, B, B, A, Down, Up, B. Now press A + B + C + Start to return to the main menu. From here you can select a starting level by pressing Left or Right.
Poacher Yell
This code requires a six-button controller. To activate, pause the game and press C, A, Down. To yell, press Mode at any time.