Sonic Mechanized is meant to serve as a prequel to Sonic Forces, happening only a few months before it. The story is that (Modern) Sonic decides to visit South Island and Greenhill Zone. He claims it's for nostalgia sake but he's heard rumors that Doctor Robotnik has once more set base there. To Sonic's dismay, the rumors were true. In fact, just as he arrives, badniks happen to be ripping apart Greenhill and mechanizing it. He finds out that Robotnik plans to transform Greenhill into a speedway, Marble into a highway, Springyard into a badnik/plant junkyard, Labyrinth as a prison for rebels, Starlight into an amusement park, and revive his old factory Scrapbrain zone. Along his way Sonic also finds out that the Chaos Emeralds found themselves back on South Island and Robotnik is using them to power his attractions. Will Sonic save the island from a similar plot done to Little Planet, or will Sonic share South Island's mechanized fate?