Impossible Mission is a classic platforming game originally developed for the Commodore 64 by Dennis Caswell. The object of the game is to stop the mad genius Elvin Atombender from launching a nuclear attack using cracked military computers all over the world. The original version is famous for having sampled speech, which was rare at the time. Elvin's opening line "Another visitor. Stay awhile - stay forever!" is well known amongst C64 players.
The player assumes the role of Agent 4125 who is sent to Elvin's underground stronghold. To reach Elvin, a nine-letter password must be found to open the control room door. The password is assembled from pieces of punch cards found all over the complex. The mission must be completed in six hours, with ten minutes taken off the clock each time the player dies.
There are 32 rooms, randomly arranged in each game and connected by elevators and corridors. The rooms contain pieces of furniture standing on platforms of varying height, most often guarded by robots. The furniture must be searched while avoiding the robots to obtain either password cards or other useful codes, such as lift resets and snoozes that make the robots freeze for a short while. There are also two code rooms that contain a music note puzzle; lift resets and snoozes can be obtained by playing back the notes in ascending order.
The robots' behaviour patterns are different in each game. There are about a dozen different combinations for their movement and firing patterns and it is usually possible - necessary, even - to determine the robot's program by observing it for a moment before trying to pass. Some robots simply drive back and forth on the platform, while others actively follow the player as far as they can and fire their zappers whenever the player is nearby. The player has no weapons except for the snoozes, and skillful jumping is needed to stay clear of the robots.
Once the punch card pieces are found, the cards must be assembled in a jigsaw-like manner. Four different pieces must be flipped in the correct orientation, combined and changed to the correct color to make up one card, which yields a letter of the password. Once the password is known, the big blue door found in one of the rooms can be opened to end the game.