WARNING: The following contains spoilers for Sonic the Hedgehog, in theaters everywhere Feb. 14.
Sonic the Hedgehog doesn't spend much time focusing on elements of the video game series other than its titular character. Instead of delving into the depths of the franchise, the film focuses on Sonic's experience being trapped on Earth and learning to love living there. Most references to the video game are minor callouts and brief shout-outs to the overall franchise.
However, the movie's two post-credits sequences tease that, should there be a sequel, the follow-up would draw more inspiration from the source material by bringing Robotnik more in line with his video game appearance and introducing a major character.
Robotnik Unleashed
Doctor Robotnik is the antagonist of the Sonic the Hedgehog film. He's also been the most consistent villain of the entire franchise, so it makes sense he would appear in the film.. The movie fleshes out Robotnik's backstory. He's a former child prodigy who was designing revolutionary technology for decades before encountering Sonic, but his standoffish attitude and arrogance repelled people. At the start of the film, he is a government-appointed researcher. Though he has some success replicating Sonic's super-speed using one of his quills, the Blue Blur is able to defeat him, sending him and his ship flying through a portal to a world of mushrooms.
The first post-credits sequence reveals that Robotnik hasn't been fully beaten and he has dedicated himself to trying to find his way back to Earth. He carries the robotic remains of his ship with him along with the quill (which still contains some power) as he explores the world.
The journey has made Robotnik even more manic, however, seemingly pushing him further over the edge than he was before. Not only does he shave his head and let his mustache fray out, he has also begun speaking directly to a rock as if it were his assistant, Stone. Robotnik is known to be a genius, so it's likely that he'll be able to find a way to make it back to Earth. When he does, it's likely that he'll, once again, target Sonic and his human friends, Tom and Maddie.
THE ARRIVAL OF TAILS
The second post-credits sequence introduces another major character from the Sonic games to Earth, setting up a potential team-up if there is a sequel. In the scene, we see a Tails make his way through a ring that has appeared somewhere on Earth. Tails, also known as Miles Prower, was introduced in Sonic the Hedgehog 2 as Sonic's sidekick and second-player character. He's a small fox with two tails that he can use as a little propeller. He's been one of the main characters of the franchise ever since, appearing frequently as Sonic's best friend and resident tech expert.
Tails' arrival hints that the movie's universe might be home to other major Sonic characters as well who, aside from Sonic and Robotnik, have been completely absent from the film. He arrives on Earth with a small tracking device. The device picks up on its target, presumably Sonic, and Tails sets off to find him. If there is a sequel, it would make sense to challenge Sonic's desire to remain happily on Earth with the chance of returning to his home-world.
This could set also Tails up to also be a co-protagonist in this hypothetical follow-up, teaming up with Sonic as he always does in the games. It also could mean that Tails -- or someone else -- is in desperate need of Sonic and his power. After all, why would Tails take the huge risk of traveling into the unknown depths of the universe if there wasn't a crisis at hand?
Opening Feb. 14, director Jeff Fowler's Sonic the Hedgehog stars Ben Schwartz as Sonic and Jim Carrey as Dr. Robotnik, with James Marsden, Neal McDonald, Tika Sumpter, Adam Pally and Natasha Rothwell.