Caverns of Mars is a vertical-scrolling shooter game originally released for Atari 8-bit computers in 1981. An unreleased prototype version made for the Atari 2600 was released on the Atari Flashback 2 in 2005. In this game, players have to control a ship to descend into the titular caverns while avoiding martian enemies and hitting the walls along the way. Afterwards, upon reaching the bottom of the cavern, the ship activates a reactor bomb, and the ship must go back up to the surface before it explodes.
In this run, Walgrey aims to get a maximum score of 999990 points, by utilizing a glitch at a certain point of the game and ends the input very early, passively increasing the score to the maximum of 999990 points.
Note that reaching 999990 points takes about 19.5 hours. The YouTube encode was sped up by 2 times after ship respawns a minute after input ends and returns to normal speed upon respawning with the score just about to reach 999990 points, while the downloadable encode has the full 19.5 hours of "gameplay."