Go to the main "press start" menu screen and type in this code L, L, L, R, R, R, RIGHT, RIGHT if the code is entered correctly you shall hear a short noise.
Enemies have health meters
At the main "press start" menu type this code Up, Right, Up, Left, Down, Right, Down, Left.
Infinite Lives
At the main "press start" menu type this code B, B, A, A, LEFT, RIGHT, DOWN, UP, if the code is entered correctly you shall hear a short noise.
Nine Objects
Go to the main "press start" menu screen and type in this code UP, DOWN, UP, DOWN, B, A, if the code is entered correctly you shall hear a short noise.
Become Invincible...