Sonic the Hedgehog 2 is the sequel to 2020's Sonic the Hedgehog, a film that had a rocky development, but would listen to fans and fix its incarnation to Sonic, resulting in it being well received, and breaking the Detective Pikachu movie's record as the highest-grossing video game-based movie, and the highest-grossing superhero movie of 2020.
Here, while Tom and Maddie are going to Hawaii to attend Rachel's wedding to a man named Randall, leaving Sonic (voiced by Ben Schwartz) in charge of the house. However, Dr. Robotnik (played once again by Jim Carey) has managed to escape the Mushroom Planet with the aid of Knuckles (voiced by Idris Elba), whom he repays by taking him to Sonic so he can destroy him. However, just as Sonic is about to be creamed, a police car rams Knuckles, revealing Tails (voiced by Colleen O'Shaughnessy, the only VA to reprise his or her role from the video games). After finding out Longclaw left a message telling Earth is the hiding place of the Master Emerald, the one thing Knuckles seeks to restore honor to his extinct tribe (as he is the last one left).
Now this is another good example of how sequels should be done. Sonic 2 is an epic film, as Sonic teams up with Tails and faces Dr. Robotnik and Knuckles. The cast from the first film returns with some new faces appearing, and the new story is awesome. Jim Carey still hams it up as the evil doctor and even Rachel gets a scene where she can be a heroine. But the best thing about this film is that it brings Knuckles back to being a serious rival to Sonic, compared to the Sega games demoting him to the role of being an idiot since the Sonic Boom cartoon. It makes me wish Sega would make notes if they saw the films, because IMHO, Paramount is basically doing Sonic better than Sega did post-Sonic Adventure 2 (it even goes as far as to give Knuckles a father, something the games would never do).
However, if there are some complaints I have, it's that this movie has some scenes that are basically imitating scenes from the first film (the Siberian lounge scene reminds me of the Piston Pit scene from the first movie, only instead of a bar fight, we get a dance off), but this is a good sequel regardless. Don't pay heed to the critics bashing it and watch it if you can and see if it clicks with you.