Start a new game on Medium difficulty. Call it .Wampa..Stompa (Case sensitive). Start in a level and as soon as it starts press pause. Now press and hold all at once C up, C right, C down, C left, L, R, Z and Left on the d-pad. While holding these down gently move the control stick left halfway, and hold all this until you hear a sound. Do the same thing with the joystick facing right, then left, right and finally left. Make sure you keep the other buttons held down during this time.
If it worked pink writing will come up, and using L, R and A you can select cheats such as 50 lives, wall ghost, next level, gravity, jump power etc. To make the menu reappear each time you go back to the pause screen C up, C right, C down, C left, L, R, Z and Left on the d-pad.