In the Sonic the Hedgehog and Mega Man crossover event Worlds Unite, Sonic Man is able to move through stopped time.
The language of French simply does not exist in the Sonic universe, rather a very similar language referred to as "Antoine-ese".
In Archie's Sonic the Hedgehog #175, Vector and Mighty can be seen playing on a Nintendo GameCube.
In Archie's Sonic the Hedgehog #188, Bean asks Sonic about marrying Sally and having mutant babies with her. Their future children are actually quite normal, they are both named Sonia and Manik Acorn respectively. Yes, it's a Sonic Underground reference.
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.
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.