Alien 3

Super Cheats
During a game, hit A, B, Y, and X on Controller Two. Then press any of these buttons on Controller One for these super cheats: A: Invincibility
B: Do more damage with weapons
X: Unlimited weapons
When you restart, a number will show underneath the large digital number in the upper-left corner. A "1" indicates invincibility; "2" indicates the damage cheat; "4" indicates unlimited weapons. The number increases when combinations of cheats are in effect: a "7" means all three cheats are working.
See the Ending
Enter this password: OVERGAME.
Passwords
Level 2: QUESTION
Level 3: MASTERED
Level 4: MOTORWAY
Level 5: CABINETS
Level 6: SQUIRREL