One of the earliest design choices of Sonic, who was a rabbit that grabbed things with his ears.
Examples:
- The original stage setup for Sonic to run through was Green Hill, Labyrinth, Marble, Star Light, Spring Yard, and finally Scrap Brain, an order that would reflect the increasingly mechanical nature of the zones and how close Sonic is to Eggman's base. The reason everything between Green Hill and Scrap Brain was changed wasn't because of its pacing, but rather due how Labyrinth would be too hard for a second level. This intended level order can be seen in the REV00 level select menu.
- The checkered wrecking ball that Eggman uses in the first boss fight was also a separate obstacle that would chase Sonic. This object is also notorious for appearing in various pre-release material such as magazine screenshots or the pilot episode of Nick Arcade. The object is present in the leaked prototype (which shows it was likely removed for having very buggy collision), and the remake has it as an object that can be placed in the debug mode.
- Scrap Brain Zone was originally called Clock Work Zone.note It also had diagonal conveyor belts, which eventually appeared in Sonic the Hedgehog 2 via Wing Fortress Zone, and a background that looked almost exactly like the foreground.
- Stealth, the same person who assisted Christian Whitehead on the iOS/Android port, made a demonstration port of the first three games to present to Sega for the DS, running well ahead in terms of frame rate before Classics Collection for the DS. Sega never responded.
- Artwork revealed
in the Sega Mega Drive/Genesis: Collected Works book shows that the original plan for the ending was for Sonic to fall from the sky, be brought down to earth safely by his scrapped bandmate, Sharps the Chicken and then pose with his friends. This sort of ending became a recurring element in the series once it was used to great effect in the sequel. - There were initial plans for a more extensive sound test mode. Sonic was the leader of a rock band that was scrapped early in development but the band was removed due to time constraints. Sonic's love of music would reappear in future games. Instead of rock, however, he became a fan of hip-hop. One of the band members would be reused as Vector the Crocodile in future titles. Additionally, at one point, according to some early Concept Art, the band members would have appeared at the end of the game with Sharps the Parakeet saving Sonic from falling in a way similar to Tails at the end of Sonic 2.
- Sonic was originally supposed to have a human girlfriend named Madonna who was a Lady in Red with short, blonde hair. There are conflicting reports as to why she was scrapped.note Considering the later reception of Sonic's "friendship" with a human princess in Sonic the Hedgehog (2006), Sega definitely seem to have made the right call here.
- Very early screenshots of Green Hill Zone featured a mountainous background◊ instead of the large lake and cascades that inhabit the final version (with the mountain ranges pushed further into the background and being relatively indistinct). The second act of Sonic Mania's Green Hill Zone features a background inspired by these screenshots.
- The Sega Mega Drive/Genesis: Collected Works◊ shows that Sonic originally collected keys instead of Chaos Emeralds which hadn't been thought up yet.
- Spring Yard Zone was originally called Sparkling Zone. It had a radically different background.
- Sonic originally had a "scarier" design that featured fangs. He was softened up under suggestion from Sega of America. His fangs can still be seen in an early promotional manga.
- Instead of Badniks, Sonic originally fought monstrous creatures. These can be seen in early Concept Art and early prototype screenshots, where only one of the creatures was left intact there. When Madonna was scrapped and the original storyline (Where Sonic was in a world of nightmares) had to be rewritten, the monsters were replaced with wackier-looking robots containing cute creatures that became Sonic's friends inside.
- Splats, a rabbit Badnik with a spring underneath it, was originally going to debut in this game but was cut from the game. It would eventually appear in various media such as the Archie Comics and Sonic the Comic before appearing in the 2013 rerelease of the game's Debug Mode and making its official game debut in Sonic Mania, before reappearing in Sonic Superstars.
- In a Sega Mega Drive/Genesis: Collected Works interview, Naoto Ōshima revealed that the sound test originally had Sonic performing Michael Jackson-like dance moves.
- According to the June 1991 issue◊ of Computer and Video Games, the game was going to be ported to home computers of the time such as the Commodore 64, Amiga and ZX Spectrum. Sega eventually scrapped the idea, presumably so that computer users of the time had a good reason to buy a Sega Genesis.
- One early concept art◊ depicts Sonic skipping across the water of a Japanese-themed underwater zone (likely an early version of what would become Labyrinth Zone) to reach a different path. While both of these concepts likely never made it past the concept stage for this game, the idea of Sonic skipping across the water to access different paths would soon be realized in the 8-bit platformers and Sonic Colors would revisit the particular concept nearly 20 years later in the form of Aquarium Park.
- According to Yuji Naka, the developers originally wanted Scrap Brain's 3rd act to contain an original background and sprite files, in order to make the final full stage truly unique. However, due to space and time constraints, they settled for reusing Labyrinth Zone's tile set with a new palette.
- There were plans for what would have been an 30th anniversary themed Updated Re-release of the game that would had been released right on the same day as the game's original release. It didn't get far, however, as it was promptly rejected by Sega when the people behind the plan pitched the idea to them.
- Beta screenshots reveal that the Marble Zone inexplicably had ufos in the background originally.
- Eventually, this version was found by a community member and had its ROM dumped and published online. This was an especially big deal because the fanbase had been searching for a Sonic 1 beta ROM with no success for over 20 years.
- The game was originally planned to have a 2 player multiplayer mode early on. However, the concept was scrapped due to Sonic Team having difficulties with trying to make the mode work with the game's speed. The mode would later be realized in Sonic the Hedgehog 2.
- In 2023, Naoto Ohshima shared more info about the very origin of the game as "Twin Stars", a story about twin human brothers who protect a dream world from Thirteen, the boss of the Nightmare World. From that concept, only the fast gameplay with smooth terrain and loops remained. He also made it clear a couple of the odd creatures shown in the artwork are meant to be a baseball bat and mitt. A fellow developer then shared pictures of his copy of Ohshima's whole pitch documentation for the project that was thought to have been lost since 1990.
