Enter "0601" as a password and ignore the invalid password message. Press Start to return to the command center. Then begin a game and hold Select + Up to move up vertically. Press Left or Right to move in that direction, or Select + Down to move down vertically. Hold Select + A to obtain the Noisy Cricket super-gun. If you entered the code correctly, a lightning bolt will appear next to the number of lives remaining.
Enter "2409" as a password and begin a new game. Pause the game and press Select to advance to the next level. Pause the game and press A to advance to the next stage within the current level.
Enter "1943" as a password.
Note: You must have a 2.1 or higher version of the Game Shark to use these codes in a Game Boy Color system.