Enter the following codes at the 'Title' screen to enable the corresponding effect. When the code has been entered correctly you will hear a confirmation sound. These codes also work on the original (Non-colour) Game Boy release of the game.
Infinite Health: Enter B, A, Up, Left, Right, Down, Start.
Infinite Lives: Enter A, Down, Up, Right, Up, A, Start.
Infinite Projectiles: Enter B, Left, A, A, Up, Left, Start.
Infinite Time: Enter Left, Left, B, Left, Right, A, Start.
View Ending: Enter Up, Down, Left, A, A, B, Start.
Sound Test: Enter Left, Left, Right, Right.
Stage Select (Password Menu): Enter Right, B, Up, Up, Left, A, Start.