Impossible Mission has the user play a secret agent – attempting to stop an evil genius. Professor Elvin Atombender is believed to be tampering with national security computers. The player must penetrate Atombender’s stronghold, racing against the clock to search the installation for pieces which form a password, all the while avoiding his deadly robots.
Once in possession of all the password pieces, the player must correctly assemble the password pieces together and use the completed password in the main control room door – where the evil professor is hiding. One finds password pieces by searching furniture in the rooms. When searching, one can also find “Lift Resets” and “Snoozes.” They are used at computer terminals. The former will reset all moveable platforms, the latter will freeze all enemies in the room for a limited time.
There are also two special rooms where additional lift resets and snoozes can be awarded for completing a musical puzzle.
The location of puzzle pieces, arrangement of the rooms and elevators, and abilities of the robots are randomly distributed each game, providing replay value. Caswell cites Rogue as his inspiration for the randomised room layouts.
The player has six hours of game time to collect 36 puzzle pieces. Every time the player dies, 10 minutes are deducted from the total time.
The puzzle pieces are assembled in groups of four. The puzzle pieces overlap, so three pieces can be assembled before the player realizes he must start over. Pieces may be in the wrong orientation, and the player may have to use the horizontal or vertical mirror images.
Additionally, the puzzle pieces are randomized in every game. A completed puzzle forms a nine letter password which allows the player to reach Professor Atombender.
Though originally developed for the Commodore 64, Impossible Mission was ported to the Apple II, Atari 7800, ZX Spectrum, Acorn Electron, BBC Micro, Amstrad CPC, NES and Sega Master System. Not all of the ports had the same features as the C64 edition, such as speech.
The NTSC Atari 7800 version has a confirmed bug that makes the game impossible to win; it places some of the code pieces underneath computer terminals, which the player cannot search (since attempting to do so will access the terminal). The bug was fixed in the PAL version.
Rumors of a bug fix for the NTSC version were put to rest when Atari formally announced the retirement of the Atari 7800 on January 1, 1992.
The NTSC Atari 7800 version was converted from the Commodore 64 version by Computer Magic, Ltd. Contractors Brian Richter started the conversion, with Arthur Krewat finishing it. Arthur states that he was able to complete the game in the final version he gave to Atari, but somehow either Atari used a previous development version for the cartridge, or that they tried to shrink the memory footprint so that it would not require as much static RAM in the cartridge.
Atari themselves tested the game and approved it, paying Computer Magic for the final product. Arthur is adamant in stating that the final version supplied to Atari was bug-free. Arthur is working on resurrecting his source code of Impossible Mission for the Atari 7800 as of December 2008, and has found that the code he supplied Atari is identical to the ROM image available on AtariAge.com. Work continues to determine how the bug came about.
The ZX Spectrum version also had this bug, although it only sometimes made the game unwinnable; not always.
Text taken from the wikipedia article at http://en.wikipedia.org/wiki/Impossible_Mission_(game)