Franchise: Sonic The Hedgehog

In 2010, SEGA de-listed every single Sonic game with anything less than an average Metacritic score so that they could not be bought new at retail or downloaded from console-based online services. This was in order to increase the value of the franchise to prepare for a "comeback". Ironically, Sonic Free Riders, released the very same year, has a below-average Metacritic score of 47 out of 100.

Sonic was originally planned to have a human girlfriend called Madonna. She would chase Sonic around, similar to how Amy Rose acts in later games.

Jon St. John, the voice of Duke in the Duke Nukem games, also voiced Big the Cat for several Sonic games starting with Sonic Adventure up until Sonic Heroes.

Sonic's shoes were inspired by Michael Jackson's boots and the color scheme of Santa Claus. Sonic's personality was inspired by Bill Clinton.

There are at least two cases of art plagiarized from deviantart.com appearing in Sonic games. A piece of art of Sonia was mistakenly added to Sonic & Sega All-Stars Racing, and some fanart that was made for a Sonic & the Black Knight contest turned out to be a replica of someone else's artwork. Sega apologized both times.

The human body has a Gene called "Sonic Hedgehog", named after the character. The gene has an inhibitor (something that stop the process of a gene) named "Robotnikinin", named after Sonic's Nemesis, Dr. Ivo "Eggman" Robotnik.

According to writer Ian Flynn, while money does in fact exist within the series, Sega has issued notes to him and other writers on the series mandating that it is not supposed to be discussed or alluded to by the characters. There are exceptions to this as certain characters' motivations are tied to making money, such as the Chaotix Detective Agency and their rent problems, or Jet's hunt for treasure in Sonic Riders.

To promote the release of the 2024 film "Sonic the Hedgehog 3", Paramount released a promotional Sega Genesis cartridge that was not only fully functional, but also included a cheat code that revealed the release date for the film's final trailer. The cartridge included three main features: "Characters" (a series of character posters that played a voice clip from said character when interacted with), "Posters" (a collection of posters used to promote the film), and "Unlock" (which starts a minigame where Sonic is chased by Shadow down an endless highway that the player cannot win or lose at). By entering the level select code from Sonic the Hedgehog 3 (up, up, down, down, up, up, up, up), Sonic will say "Hey, I said no cheat codes! ...Okay, just this one." before booting the player back to the main menu. A fourth option, "Trailer?", is unlocked, which revealed the release date for the final trailer as November 25, 2024, before booting the player back to the main menu once again.

In Archie's Sonic the Hedgehog comics, the G.U.N. Commander (who was unnamed in the games) was given the name "Abraham Tower". According to writer Ian Flynn, the reason he was given a name was because he "didn't want to be trapped by calling him 'Commander' or 'sir' every stinkin' time". The name (originally used by a character from a fan-made comic that Flynn never finished) was meant to evoke an idea of authoritative power: "Abraham", whether in regards to the biblical figure or the U.S. historical figure, lends itself to the notion of an influential leader, and "Tower" was in reference to how he was "tall, rigid, standing over all others". Although the name was exclusively used in the Archie comics, it would later be made canon to the game continuity when it was used for the character in the webseries "Sonic X Shadow Generations: Dark Beginnings", which was also written by Flynn.

Due to the cancellation of the animated series "Sonic Underground", its storyline was left unresolved. However, staff members involved in Archie's Sonic the Hedgehog comics had considered finishing the storyline: writer Ian Flynn had thought about writing a new story that could serve to wrap up where the original series left off, but felt it would be "stepping on the original creatives' toes," and that even if he was allowed to do it the story likely wouldn't see the light of day for at least two years. Originally, "Sonic Universe" issue 50 was intended to be the official epilogue for the show, with a preview cover being released. However, the epilogue was cancelled, and the issue instead featured a story centered around Metal Sonic.

In early 2013, Ian Flynn revealed that material from "Sonic Underground" was off-limits: this was the reason why the epilogue was put on hold. He also stated plans to include the epilogue as part of "Lost Hedgehog Tales", a written document featuring Sonic comic material that will no longer be used, suggesting that the epilogue was no longer possible. In June 2017, any chance of a "Sonic Underground" epilogue by Archie was precluded when Sega announced that the comics produced by them had been cancelled.

In the 2020 Sonic the Hedgehog film, Sonic’s disdain of mushrooms could be a jab at his rivalry with Mario in the 90s. This is reinforced in the Thai dub of the film, where the joke about Tom saying that Sonic won’t be the only “fungi” on the mushroom planet is replaced with “at least you can have a mushroom forever,” to which Sonic replies with “No. I’m not Mario”.

Nintendo possibly “returned the favor” in 2023’s The Super Mario Bros. Movie, where the Super Mario Bros. Plumbing advertisement features a map with one of the landmarks listed as “Mushroom Planet”.

In the early 2010s, Pop, a British TV channel that syndicated DIC's Sonic the Hedgehog cartoons, had the fanmade game Sonic on Clouds avaliable on its website.

Dan Slott, a comic book writer best known for his work on Marvel Comics such as "The Amazing Spider-Man", "Fantastic Four", and "Silver Surfer", wrote for two issues of Archie's "Sonic Super Special" series as part of its "Zone Wars" storyline. Despite these being his only works for the comic, he did make one notable contribution: Zonic the Zone Cop, an alternate reality version of Sonic who monitored all realities in order to maintain balance across the various Zones, though allowing other people to appear in other Zones when they are needed. In November 2022, in response to various fan questions about Zonic, Slott noted that he was willing to collaborate with Sega to bring him back, and had no protective hang-ups over the character unlike an unspecified Sonic creator who was "super protective of all the characters he's created over the years to the point where SEGA doesn't want to use ANY of them in other media" (likely referring to legal issues surrounding former writer Ken Penders).

In the aftermath of Ken Penders' lawsuit against Archie Comics that led to their Sonic the Hedgehog comics getting rebooted, a common misconception among fans is that one of the characters he acquired the rights to as a result was Fiona Fox. This is not actually true: while Penders did help "recreate" the character, the initial character (an Auto-Automaton dubbed "Auto-Fiona"), was created by another former writer, Michael Gallagher. While it's uncertain if that he means he owns the character, Penders has stated that he did not want to claim a character that he did not create.

Quik & Silva features many plagiarized characters as duplicated enemies, including characters from Nebulus, Bubble Bobble, Contra, and The Great Giana Sisters. Among these characters is Sonic the Hedgehog, whose first title had not released at that point, technically making it Sonic's first appearance in a home console video game, even if unauthorized and predated by the arcade game Rad Mobile.

Throughout 2023, Sonic Channel released a monthly series of wallpapers titled "Otherworld Comedy", each one featuring a what-if scenario involving an established character from the Sonic series, alongside another chosen by the community. The stories are comedic in nature, having unlikely scenarios involving the cast of characters.

Notably, the April wallpaper (centered around Silver the Hedgehog), "Story Act 4: In the Veil of Darkness", featured Princess Elise as the chosen character. This not only marks her first appearance in mainstream Sonic media since her cameo in Sonic Riders: Zero Gravity, but is also the first work she played an active role in since her debut in Sonic the Hedgehog (2006). A cutscene in the latter game, called "The Talisman", is referenced in the story when Silver gives Elise the blue Chaos Emerald, calling it a "lucky charm". Additionally, Elise herself received a slight redesign for her appearance here, being depicted in a more cartoon-esque style rather than the realistic design she had in her debut game.

Upon the release of Sonic Chronicles: The Dark Brotherhood, Ken Penders, a former writer on the Archie Comics Sonic comics, sued Sega and EA for supposedly using Sonic character concepts he had independently trademarked prior - particularly the Nocturnas Clan, a futuristic echidna tribe which he deemed as too similar to his own Dark Legion, a futuristic echidna technocracy. This lawsuit came months after Archie Comics filed their own suit against Penders due to a breach of contract after the trademarking, causing Archie to allow their contract with Sega to expire so they could negotiate new terms for the rights to create Sonic comics. This legal fiasco ended in Archie settling the case with Penders, losing the exclusivity to produce Sonic comics after negotiations with Sega, and causing them to write the "Super Genesis Wave", a super-charged energy blast utilizing the Chaos Emeralds that acted as a massive continuity rewrite where over 500 original characters and concepts created by Penders and other writers for the Archie Sonic comics were retconned. The Sega case on the other hand ended in a stalemate due to the statute of limitations, and will not be able to continue unless Sega uses characters from The Dark Brotherhood again.

Prior to doing official work on the Sonic the Hedgehog franchise as one of its writers/artists, Evan Stanley worked on a fan comic called "Ghosts of the Future" based on the series. Set in an alternate reality where Sonic and his friends are defeated by Dr. Eggman with the aid of a mind-controlled Shadow, the comic featured Silver the Hedgehog as the main character, tasked with restoring the seven Chaos Emeralds that were removed from time as a last resort. After being brought on to do official work on the franchise, the fan comic has been referenced on two occasions in official Sonic comics. The first was in issue 257 of Archie's Sonic the Hedgehog comic, which featured cameos from Richard and Deborah Erin (Silver's parents in the comic) during the scene where Rotor is directing rescue operations outside Twinkle Park (note that they are slightly recolored in this scene). The second time was in issue 64 of IDW's Sonic the Hedgehog comic, which featured cameos from Vanice the Hedgehog and Sicily the Hedgehog (Silver's sisters in the comic) during the scene where Silver and Whisper are trying to confront Duo.

"Sonic.exe" is a creepypasta story originally written by JC-the-Hyena, a user on the Creepypasta Wiki, about a cursed CD-ROM version of the first Sonic the Hedgehog game, notable for its malicious depiction of Sonic, giving him black eyeballs with glowing red pupils. The story became popular partly through a genuine appreciation of the story's content and scariness, and from those mocking the extremely poor quality of its writing, which has also been described as amateur and cliched, and later led to it being removed from the Creepypasta Wiki. Sonic.exe received two lesser-known sequels, a rebooted story in 2017, many unofficial games based off of it, as well as other tributes and parodies. JC-the-Hyena would later resign from authoring new Sonic.exe projects after multiple allegations of pedophilic and predatory behavior surfaced in 2021, with the story's fan communities taking control of it since.

The story became so popular and attached to the wider Sonic franchise that the official Sonic the Hedgehog Twitter account has referenced the story on two separate occasions. The first was on January 13, 2017, where they posted a video of Sonic standing in Green Hill Zone as a black recolor of Big the Cat passes him by, changing him and the environment to something more akin to what is depicted in the story. The second was on April 14, 2021, where they posted an image of a pile of Game Gear Sonic titles, with Sonic.EXE being hidden within the pile.

In issue 21 of IDW's Sonic the Hedgehog comic book, two characters on page 20 resemble Marinette Dupain-Cheng and Adrien Agreste, the main protagonists of the animated series "Miraculous: Tales of Ladybug & Car Noir". These characters would later appear again in "Sonic the Hedgehog Annual 2020" on page 7, itself a reference to the events of this issue.