The sequence of Dr. Robotnik getting his head shaved happened on set, as Jim Carrey stated it took a year and a half for him to grow out his hair and had actor Lee Majdoub (Agent Stone) cut his hair. Majdoub was terrified to shave Carrey's head on camera.
After their initial race, Knuckles and Tails are there waiting for Sonic tapping their feet with their hands on their hips. This is the same animation in the games if you leave your character standing for too long
Following the release of Sonic the Hedgehog 2 (2022), Jim Carrey announced that he was considering retirement, and said he would only return to acting if "the angels bring some sort of script that's written in gold ink that says to me that it's going to be really important for people to see." Producers Neal H. Moritz and Toby Ascher stated that Carrey's role as Dr. Robotnik would not be recast if he followed through with his plans, but remained hopeful that he would be willing to continue the role if the script was satisfactory to him. They would eventually send him a script for this film printed with 24-carat ink. In February 2024, he was confirmed to reprise his role, making it the first time Carrey has starred in more than two films as the same character.
Sonic says Keanu is his favorite actor in Sonic 1 when they are watching the Movie "Speed". Keanu is the voice of Shadow in Sonic 3
The film makers of the prior movies have mentioned playing both Sonic Adventure 2 (2001) and the Shadow the Hedgehog (2005) solo game for inspiration. The film is also inspired by narrative elements from the Saturday morning animated television series Sonic the Hedgehog (1993).