Sound Mode
To listen to any of the game's music and sound effects, simply hold A and B on the title screen and then press Start. On the Sound Mode menu, press up or down to move the cursor and make your selection, B to play the music or sound, and A to stop. There are 14 music tunes, 24 sound effects, and a bonus medley tune. To return to the title screen, press Start.
10 Lives Code (30 Lives in the Japanese version)
On the title screen, press Right, Left, Down, Up, A, and B. Afterward, choose your game mode and press Start. You (as well as the other player if there is one) will begin the game with ten lives (thirty if you're playing the Japanese version) instead of just three. You will also get ten lives for each continue.
Stage Select (Japanese version only)
On the title screen, press and hold Down and Select. While holding the buttons, press Start and you will be taken to a Stage Select screen. This works only in the Japanese version.