Metal Gear 2: Solid Snake

Hideo Kojima's official sequel to the original Metal Gear and Konami's final MSX2 release, Metal Gear 2: Solid Snake greatly expanded upon the original formula with a more elaborate A.I. behavior for enemy soldiers (who were given a wider field of vision, better hearing and the ability to patrol different screens in real time), the ability to crawl under tight spaces and an extensive narrative that has become part of Kojima's personal trademark. The game later served as the template for the original Metal Gear Solid.

Starring the unlicensed likenesses of Mel Gibson, Tom Berenger, Richard Crenna and Sean Connery (unless you're playing one of the later ports, where everyone looks just like they did in the original Metal Gear Solid).

Sound Test
Equip the cigarettes and then go to the radio screen. Set the frequency to 140.07 and the game will play a random music track. Change to another frequency and then switch back to 140.07 to play a different track.

Debug Mode
Metal Gear 2 has an extensive debug feature that's been made inaccessible in the retail version. The only way to unlock it is by opening the ROM image with a hex editor and changing the value placed at offset to a, which will remove the instruction preventing its access.

This can also be done on an actual MSX2 with a MegaRAM cartridge containing the ROM, although the procedure is a bit different. Go to page of the ROM and change the value placed at position  to a

Warp Keys
The following keys will transport the player to the indicated location when the game is running on debug mode.