Enter the "CONTINUE" menu, then press B, Right, Start, Right, Right, Select, Right, Left, Right, Right, Right, Left, Select, Left, Right, Select.
A two-digit number will appear at the borrom-right corner of the screen. Press A to cycle from $00 to $1A, press B to return to continue menu. Numbers from $00 to $19 are level numbers, where you start when loading any game. Number $1A will disable the background music.
There exists an additional credit meant to be displayed in the final credits roll,
. Use the Game Genie code
ILVOVXGU to restore it.