Hold Reset and power on the Atari 2600. Select game 1 and begin game play.
Pause the game and press Right, Right, Right, Down, Circle, Left, Down.
Double Fire Power
When you first turn the game on, simply press GAME SELECT several times, hold down GAME RESET.
Switch the console off and then back on again then release GAME RESET.
This should give you double fire instead of one at a time.
Game Shark Codes
North American (NTSC) version
Always have vertical burst:
Always have horizontal right:
Always have horizontal left:
Always have diagonal burst:
Hold A + C, then press Start at the title screen. Quickly press B, A, C during the short pause that occurs before the first level is displayed. A level selection screen will appear.
At the main menu, choose either one or two players and press Circle (instead of X) to begin the game. An option screen that allows anylevel, including planet Mercury with a new power up and an "Alien World" featuring the best background in the game.
Pause the game and press Down, Left, Circle, Down, Right, Right, Right.
Classic Mode And Credits
Enter the "Level select" code, choose level 00, and complete it to unlock an ending, classic mode, and credits. Press Right when choosing then number of players to access classic mode. Enter the options screen to access the credits.