The characters introduced at the end of Sonic the Hedgehog 3 are exciting, but they will create a major problem for the fourth film. The story of Sonic 3 follows Sonic, Tails, and Knuckles, who are recruited by GUN to take on Shadow, who escapes from Prison Island at the beginning of the film. Shadow proves to be too powerful for them to fight alone, so they end up reuniting with Jim Carrey’s Ivo Robotnik. At the end of Sonic the Hedgehog 3, Gerald Robotnik, Ivo’s grandfather, emerges as the true villain and is dead set on destroying the world.

https://screenrant.com/sonic-the-hedgehog-3-new-characters-problem-sonic-4/