Thanks to a large amount of Executive Meddling, there is so much of What Could Have Been.
The 16-bit version
Brenda Ross' mockup of the cut Sand Shower Zone.
- The original plot synopsis was to have Sonic and Tails to chase Dr. Eggman throughout Westside Island as they time travel. A similar idea was later retooled for Sonic the Hedgehog CD.
- Originally 18 Zones were planned for the game, only to be cutdown to 11:
- The most famous of all is Hidden Palace Zone, which was one of the first stages developed and one of the last cut. According to Yuji Naka, the stage would've been entered by collecting all the Chaos Emeralds which is where Sonic could then transform super.
- Ocean Wind would've been a coastal area with huge rock structures that Sonic could presumably run on. Another scrapped stage called Tropical Sun has an extremely similar design and feel.
- Wood and Secret Jungle are both very similar in concept, that being heavily forested areas with the former being playable in two prototypes, albeit extremely incomplete.
- Sand Shower (often thought to be called Dust Hill until the release of a "Pre-Beta" deconfirmed it) was a extremely yellow desert and cacti; another stage called simply "Winter" would reuse the same tiles as Sand Shower, but changed to blue and Christmas trees in place of cacti.
- Rock World is referenced multiple times in concept art, but no actual sprites exist.
- According to its name, Blue Lake would've taken place in a lake. Humorously its intended slot ($06) was overwritten with Wing Fortress in the final.
- Act 3 of Metropolis Zone was intended for another stage called Cyber City, or Genocide City in some prototypes as the partially Japanese staff apparently didn't know what genocide meant.
- Olympus and Tropical Plant is referenced on an early map, but no concept art for it is available.
- Emerald Isle has concept art available and looks extremely similar to Aquatic Ruin; it's possible Emerald Isle would've reused Aquatic Ruin's tiles (similar to Emerald Hill's tiles being reused for Hill Top).
- Blue Ocean would've been an underwater level with caverns. Its only piece of concept art shows it would have tunnels similar to the ones in Labyrinth Zone.
- Madness Mountain would've been a castle on a mountain.
- Death Egg would've had two acts, but was cut down to one in the final.
- Early versions of Sonic 2 featured different sprites for Sonic which looked a lot closer to the original.
- The Nick Arcade prototype had a Scrappy Mechanic where running into walls fast enough would cause Sonic to bump off. Considering this is a Sonic game, this was obviously removed. Sonic the Hedgehog (2006) has a similar "feature".
- Emerald Hill was originally titled Green Hill, Wood was Woods, Wing Fortress was Sky Fortress, Aquatic Ruin was Neo Green Hill, and Mystic Cave was called Dust Hill.
- Earlier versions of Casino Night had a completely different theme, being pink/blue instead of golden.
- The Simon Wai build has very different takes on the game's music, with most of them matching up with Masato Nakamura's demo versions (especially Casino Night).
- In Beta 4 and 5, the Wing Fortress boss was capable of destroying the spike platforms, which respawn after three seconds. Clearly someone thought this was a Scrappy Mechanic and it was removed in Beta 6.
- Tails was originally meant to be a tanuki, but was changed to a fox to avoid confusion with Super Mario Bros. 3. His original name was also Miles Monotail.
- It was possible in earlier prototypes for players to explore the entire game in two player mode, though often produces buggy or downright unplayable results due to how splitscreen rendering handles tile drawing and object loading. As a result, the final game only allows Emerald Hill, Casino Night and Mystic Cave to be played in self contained races. Some leftover coding to optimise Hill Top's graphics in splitscreen suggest it was still planned for vs mode as well.
- One of the planned sidekicks for Sonic was a turtle named Boomer. Boomer's shell could have protected him from enemy fire and Sonic could have rode it across spikes and lava, but if Boomer were flipped on his back, he would be vulnerable to enemy fire and have to have Sonic flip him back up.
- According to Craig Stitt, there were plans to invoke New Work, Recycled Graphics with a pitch known as "Segapede" later known as "Astropede". His idea would have involved a robotic centipede named "Zipp" who was stated to be one of Eggman's creations turned rouge (later seen in Sonic Adventure with E-102 Gamma and Sonic Heroes with both E-123 Omega and Neo Metal Sonic). Of the stages seen in the pitch, one of them reuses graphics from the Hidden Palace Zone.
The 8-bit version
- A leaked Auto Demo build includes a music track not seen in the final. Additionally, Green Hills had white dirt and Underground looked incredibly different.