Moon Master is the video game the Mooninites give Meatwad in Moon Master. It appears to be 4-Bit, and it resembles games for the Atari. Unlike real games, Moon Master is very easy, because it's just a scam to get Meatwad, Shake, & Carl to buy merchandise from the game. Its boss is the Gorgotron, who is an actual creature on the Moon, who kills the Mooninites when they go back there.
The Mooninites used this game for a scam, it's unknown if they created it or not though. They told anyone who beaten level four that they are the Moon Master, and sold the Moon Master a bunch of unnecessary junk.