One piece of official Super Mario Bros. Movie concept art depicts Otto the Minion acquire a super star item and go on a mad dash across the mushroom kingdom, including a panel where Luigi is about to get his cock and balls melted by Dr. Eggman from the Sonic the Hedgehog series.
Development artwork for Sonic the Hedgehog 2 depicts Super Sonic drawn in a pose reminiscent of Goku the moment he turned into a Super Saiyan for the first time in chapter 317 of the Dragon Ball manga, "Life or Death".
Prior to the release of Sonic the Hedgehog (2006), a file leaked online containing the game's script and early character write-ups. Silver's overview is wrapped up with the following sentence: "Essentially, think Trunks from Dragon Ball Z."
According to Ian Flynn in the 9/16/19 BumbleKast, Sally and Nicole were intended to have a romantic relationship post-SGW. This wasn't met with the book being canceled, but it would have made them the first (if not, one of the first) bisexual Sonic the Hedgehog characters.
In Archie's Sonic the Hedgehog comics, Knuckles died, entered the afterlife, and was sent to be resurrected 3 issues later.
Amy Rose seems to be the only character in the main Sonic the Hedgehog cast who can handle a casual punch from Knuckles.
Scott Pilgrim's high school band "Sonic & Knuckles" is a very subtle reference to the 1994 Sega Genesis game Sonic & Knuckles.
Sonic the Hedgehog does not know what hedgehogs look like.
Whisper the Wolf's design began with an in-game custom character in Sonic Forces. From there, she would gradually evolve into her final look.
Tails is very discontent with the fact that Eggman has settled on making Tails Doll rather than a Metal Tails. Moreover, this suggests that he finds Metal Sonic and Knuckles to be particularly cool.
When robots or lackeys fail, Eggman uses his built-in command grab
In 2015, it was revealed that Ian Flynn, Tracey Yardley!, and Ben Bates of Archie Sonic the Hedgehog fame had pitched a line of Super Mario comics to Nintendo. It was ultimately rejected. Allegedly, Mario was also intended to cross over with Sonic and Mega Man in comic form.
Knuckles the Echidna's father dies of pancreatic cancer in the Archie Comics.