Temporary Invincibility
Start the game and look for five items on the roof. Pick up the itesm in this order: Cake, Hammer, Earth, Apple, Tap (CHEAT). You are now invincible and will remain that way for 10 minutes.

Secret Level
In the first level, go as far right as possible. Now climb the tower all the way to the roof, and walk through the wall to the left.

Refill Power Meter
Pick up these items in order to refill your power meter: Penguin, Oil can, Wine glass, Earth, Racket.

More Options
From the title screen, hold Down-Left + A + C and press Start. Release everything and you'll see a new menu with level select, sound test, and controller configuration options.

Level Skip
Activate the Invincibility code, then pause the game and press A, A, A, A. Unpause the game and you'll be transported to the exit. Note: on some levels this will put you in odd places where you'll have to reset the game

Level Select
Activate the Invincibility code, then complete the level normally. All levels will open and you'll be able to play them in any order.

Infinite Lives
To get infinite lives in the sports level, pick up items in the following order. Lips, Ice cream, Violin, Earth, Snowman.

High Jump
Press C + B + Down and wait a few seconds. Release these buttons and you'll jump much higher than normal. The longer you hold your buttons down, the higher you'll jump