Enter the following codes at the Setup Menu
Demo:Left, Right, Up, Down,
LC, RC, LC, RC x3 50 Lives Up, Down, Down, Left, Right, Left
50 Lives: Up, Down, Down, Left, Right, Left
Game Boy Mode: Up, Down, Right, LC, Down, Up,
Left, RC, Up, Down
Level Select: Down, Up, LC, Down, LC, RC, Down,
RC
Enter the following codes while playing the game
Flame Thrower: Down, Right,
Down, Right, RC
Four Way Fire: Down, Down, Up, RC
Radiation Spray: Up, Down, RC, LC
Shield: Down, Left, LC, RC
Speed Up: Left, Left, Right, Right, UC
Three Way Fire: Right, Right, LC, DC
Two Way Fire: Up, UC, Up, UC