Sonic Movie 4 Idea (Spoilers for Sonic 3)
Bonkers Idea, But Hear Me Out:
Have Amy come from a future where Metal Sonic managed to take over the world Skynet (Neo Metal Sonic) style using a techno organic virus that transforms its hosts into robots controlled by Neo Metal, with her being part of a resistance of Freedom Fighters that includes her and a few others like Sage and Silver, with Amy being sent back to stop the creation of Metal Sonic with the aid of the actual sonic. However, during it, Neo Metal would attack, finding out about their plans and infecting Sage and Silver, then sending his drones back in time to stop Amy and Sonic, including the newly converted Sage and Silver.
Have Sonic, Amy, and the others track down Robotnik, suspecting her survived and was responsible, only for us to get a movie version of Mr Tinker, with it being an Amnesiac Eggman whose now just this chill and kind inventor who willingly goes along with Amy and Sonic despite not really knowing what's going on.
Have it be revealed that Agent Stone of all people created Metal Sonic, following old blueprints drawn up by Robotnik during his isolation, creating metal to avenge him, with Metal then gaining sentience with this version of Metal later becoming Neo Metal.
Have Robotnik gain his memories back with the help of Agent Stone. Meanwhile, Neo Metal manages to travel back in time himself, then connects to and converses with his beta version, finding their coordinates and leading his forces to their location to their location in a last attempt to stop Team Sonic, with Eggman and others also working to try and take out Beta Metal while Team Sonic fights Metal and his forces. Because, if he can't be the one to take over the world, nobody can