While Worlds Collide drastically effects Sonic's World (causing the SGW), it did nothing to Mega Man's world. Worlds Unite however, does the opposite, as it explains how Xander Payne became Mr. X, while being ultimately inconsequential to Sonic's World.
@LandofHartbjorn Actually the respective heroes and villains vaguely recall what happened, being aware of each other without needing to rewrite time and space; the supporting cast though, seems to have no recollection at all.
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.