Underground Mission is a puzzle platformer that's possibly based on the 1965 Chinese film Tunnel War, though it's probably most notable for being one of Inventor's few from-scratch games that proceeded to be included in many plug 'n plays, and other bootleg consoles.
Unused Rest of the Game#
Due to a programming bug, the entire game past Mission 1 is inaccessible on the plug 'n play version and therefore unused;1 a collection sound plays when a soldier is rescued, but the stage results screen is not triggered. This does seem to be unintentional, as the manual of the earliest system seen with it, the Power Joy Navigator, mentions that the player must rescue the captive soldier.
Unused Graphics#
Original Publisher
As with all plug 'n play versions of games by Inventor that were released on cartridge, the Shanghai Paradise Science & Technology Co. logo is present in the CHR data. This is presumably used in the original release of the game, but said version has yet to be found.
Player
Additional attack sprites for the player.
Enemies
Sprites for the officer's death animation.
Graphics for the officer ducking. It also seems he may have carried a knife rather than a machine gun at some point in development.
Items
Graphics for an alternate design for the medal, as well as a machine gun never found in-game.
Bullets
Two alternate bullet graphics.
Results Screen
Sprites for the rifleman and for soldiers getting hit, both going unused.
More interestingly, there are also several enemy types that are nowhere to be seen in-game and have no other graphics for them in the ROM. Some of these include infantrymen wielding rocket launchers and flamethrowers, as well as attack dogs and even a tank.
There's also what seems to be a sandbag.