Movies News Talk
One key reason why Amy is speculated for Sonic The Hedgehog 3 is because of how important she ends up being during Sonic Adventure 2. During the game's Last Story chapter, Space Colony ARK, the space station where Shadow was made, is automated to crash into Earth, something that could cause a devastating apocalyptic event. Amy pleads with Shadow to help save humanity, triggering a memory where he realizes that had been his promise to Maria before she died. Without Amy's words, Shadow never would have assisted Sonic in stopping the ARK from destroying the planet.
While Amy is important to Shadow's character development in the games, the lack of news about her appearing in Sonic The Hedgehog 3 makes it seem like she might not be part of the main story. However, given her longevity in the franchise coupled with how prominent she becomes in later games, it would make sense for the movie franchise to introduce her sooner rather than later. Even if Sonic the Hedgehog 3's game inspiration doesn't guarantee her a major spot in the story, she could still appear in the film thanks to one unexpected medium.
While anything could happen in Sonic the Hedgehog 3's Post-credits Scene, Amy's introduction would be the perfect transition into the next adventure. Instead of appearing during the movie proper, her debut could be saved for the film's post-credits scene. Even though this would cut her from Shadow's story in the movie universe, it would give her a spot in the movie while explaining why she hasn't been confirmed yet. It could also potentially set the stage for an adaptation of the game she debuted in.
Amy first appeared in the 1993 game Sonic Cd, focusing on Dr. Robotnik using artifacts called Time Stones to enact his newest villain scheme. The game also introduces Metal Sonic to the franchise, Sonic's robotic rival and one of his most classic antagonists. Because of how important concepts of the game became to the Sonic the Hedgehog universe, it wouldn't be surprising for the movies to mirror this with Amy's introduction. Instead of being part of Shadow's story, it's possible she instead ushers in a Sonic CD adaptation for Sonic the Hedgehog 4.
If Amy's debut coincides with a Sonic Cd adaptation, Sonic the Hedgehog 4 could more readily position her as a new hero on the team. This would allow her enough time to form an attachment to the group, such as her crush on Sonic, while being a direct force against the new threat they face. Her appearance could also offer a more stable ground for Metal Sonic's debut, perhaps giving her a more active role in the story when adapted to the big screen.
In addition to her appearance, Sonic the Hedgehog 4 could establish Metal Sonic as coming from the quill still in Dr. Robotnik's possession. This would make the metallic version of the franchise's namesake all the more threatening, perhaps requiring Amy's help to defeat him. By appearing in the Post-credits Scene of Sonic the Hedgehog 3, Amy would become an even more vital part of the story than if she shows up in the movie proper. This could help establish her in a more nuanced context, not just for the fourth movie, but for other adventures that follow.