Prerelease:Sonic the Hedgehog (Genesis)

Creating Sonic
Before the release of the Mega Drive, Sega wanted to make sure that their new console would sell as well as the NES. To do so, the company held a competition throughout all of its branches to create a new mascot that would replace Alex Kidd. Many concepts were created, such as a wolf wearing an American flag t-shirt and an odd-looking jester. Eventually, it came down to four designs created by Naoto Oshima, who had previously worked on the Phantasy Star series. These entries included a grey rabbit who could throw things with his ears, an armadillo, a fat mustached man wearing pajamas that was based on Theodore Roosevelt, and a hedgehog character called Mr. Needlemouse.

It was decided that the hedgehog character was the best of the lot, and was redesigned into Sonic the Hedgehog. Some of the other designs were reused later; the mustached man became the basis for Dr. Robotnik's design, while the rabbit's ability to throw things was retooled into Ristar.

Early Ideas
Early in development, several ideas for Sonic 1 were created by Naoto Oshima. One of these ideas was Madonna, a human love interest that was described by Naoto as a "male fantasy" who would chase Sonic around. There are two stories behind her being scrapped. The first one, told by Sega of America project manager Madeline Schroeder, says that she was responsible for removing Madonna in order to make the game easier to sell in western markets. The second story, told by Yuji Naka, says that Madonna never got past the concept stage due to how she would have made Sonic 1 more similar to Super Mario Bros.

At the same time that Madonna was being created, Oshima created a drawing showing many enemy concepts. They included a six-fingered hand, a purple creature with a large jaw and yellow gloves, a walking cannon and exclamation mark, a flying hand similar in appearance to Bat Brain, a large white ghost, and a bee-colored Robotnik. The development team thought that Robotnik's design was the best out of the bunch, so the other concepts were scrapped. The purple creature did make it to a prototype of Sonic 1 shown at the Tokyo Toy Show, but had its colors changed from purple and yellow to blue and red.

Another concept that was scrapped was the Sonic the Hedgehog Band. Originally, there was a full sound test where Sonic breakdanced to his band playing music, which included an early version of Vector the Crocodile. Due to time constraints, the idea was scrapped, and the sound test ended up being on the level select. The room that the graphics took up on the ROM, around an eighth of the cartridge, was replaced with the "Sega!" chant heard at the beginning of the game.

1990 Tokyo Toy Show
The very first time Sonic 1 was shown to the public was at the Tokyo Toy Show in June 1990. This build of the game shows an early version of Green Hill Zone, with large mountains and some odd blue structures in the background. It had seven layers of parallax scrolling, including trees and giant rocks in the foreground. Sonic had a different standing pose where his arms were more spread out. After running for a bit, he would eventually come to a large sign with "YOU ARE WELCOME SEGA SONIC" written on it. Sonic would eventually reach the end of the level, where "Debut approaching" was written in Japanese.

At one point in the demo, a blue creature wearing red gloves jumped over Sonic. This creature was one of the original ideas for an enemy that Sonic would have to fight, and was seen in a piece of concept art featuring Madonna, Sonic's scrapped love interest.

Sonic
A prerelease screenshot shows Sonic jumping and doing a fist-pump after clearing an act. The sprites for this animation are still in the final game.

This screenshot shows an injured Sonic being knocked back further than he does in the final game.

Title Screen/Level Select
The title screen went through some changes. The title screen of the build shown at the Tokyo Toy Show has "SONIC" in smaller letters and is missing the background. The prerelease screenshot shows the "PRESS START BUTTON" message that was mistakenly disabled in the final game.

The stage select once used a bluish-grey palette instead of a sepia-tone one. Some acts have Xs listed after them, and Final Zone is missing from the level select. It's possible that either the level wasn't started on when this screenshot was created, or Clock Work Zone Act 3 was an early version of Final Zone.

Other
Many prerelease pictures of Sonic 1 have the HUD display the Ring meter as "RING" instead of "RINGS".

The title cards had a minor addition in the prerelease photos; a small period can be seen after the word "ACT".

A couple of prerelease screenshots show an early version of debug mode where numbers indicating Sonic's position are placed at the bottom of the screen.

Green Hill Zone
A large boulder was planned to have been in Green Hill Zone, which Sonic could have pushed around. It can be accessed in the final game by debug mode, but it cannot be placed. The boulder's sprites were reused for the first boss of the game. The sunflowers seen in Green Hill Zone were planned to be purple-colored like the flowers in the game's good ending.

This screenshot, along with others, show that Green Hill Zone's background was more featureless at one point.

Marble Zone
Pictures exist of a very early version of Marble Zone, with flipping platforms, a more segmented ground, chunkier lava, and larger ruins.

In many prerelease screenshots, and in the background of a scene in Wayne's World, UFOs are seen spinning in the sky in Marble Zone. The Spikes badnik was also seen, and can be spawned with debug mode. This area's moving platform is different between the prerelease and the final game. A screenshot of the area near the end of Marble Zone Act 1, showing unused sideway spikes. It was replaced in the final game with the moving green blocks seen throughout the level. However, the object, code, and sprites for the spikes still exist in the final game, and will work as intended if it's placed by a level editor. The spikes that are used in this area are wider in this screenshot, and the flames coming from the torch in the background are missing.

In this screenshot, the green pillars that crush Sonic are missing. The area to the right is different in the final, and the lava has a less polished appearance.

Spring Yard/Sparkling Zone
Early in development, Spring Yard Zone had a completely different look, and was called Sparkling Zone. The foreground was the same, but the background showed a large city with flashing lights and signs. The pillars were colored both purple and blue in the prerelease screenshots.

This area near the starting point in Act 1 once had spikes spinning around a bumper, presumably removed due to making the part too difficult. Interestingly, this obstacle was kept when Sparkling Zone was changed into Spring Yard Zone.

Further into Act 1, this part of Spring Yard was completely changed in the final!
 * A set of spikes, a lamp block, and a pillar were removed.
 * A Motobug is seen in this picture. The only act that they appear in Sonic 1 is Green Hill.
 * The Roller badnik is purple in this screenshot. It was colored blue in the final game.
 * The flashing blue lights in the background are simpler.

Labyrinth Zone
All of the known prerelease photos of Labyrinth Zone are of the stage in a very early state; it was shown to have been devoid of objects and, sometimes, didn't even have a background. However, later screenshots of the level gave it a rock-filled background. The early version of Labyrinth Zone also included smaller versions of the crystals seen in the final game.

Star Light Zone
Prerelease photos show that Star Light Zone had a less blocky appearance and used its truss tiles more often, giving it a more "under construction" look. The area containing four monitors at the beginning of Act 1 had two pits and a breaking platform at some point of development.

Act 2 once had a very different opening area, which made it look less empty. The row of springs in Act 3 originally had a second row facing downwards.

Scrap Brain/Clock Work Zone
Scrap Brain Zone was originally called Clock Work Zone... or Clock Ork Zone, since the title card font is missing the letter W. Sonic started this zone indoors, and the background was colored the same as the foreground.

Diagonal conveyor belts were once used in Scrap Brain Zone, but were probably replaced with the spinning platform conveyors in the final.

A prerelease photo of Scrap Brain shows that the tunnels with the large beams that move back and forth were originally zig-zagged.

Videos
gtaM0Xme21k This video (slowed down for better visibility) contains two versions of Sonic 1 that were shown at the 1991 Consumer Electronics Show. They feature some notable differences from the final, including: The second version of the game, shown in the latter half of the video, changes GHZ's water color to the final's.
 * A different version of the Ball Hog badnik, where it faces towards the player and throws a bomb on both sides, similar to Crabmeat.
 * Monitors that cycle between the various powerups, including the unused Robotnik face and possibly the goggles (barely visible on the first monitor as it scrolls offscreen).
 * The early debug mode which replaces Sonic's lives meter
 * A minor aesthetic change is present: the water and sky colors of Green Hill are the same (like the title screen).

vDP9jfIwe7A In the film Wayne's World, after Wayne interviews the owner of Noah's Arcade and mocks him in the process, a TV in the background displays a commercial for the arcade at the 1:53 mark. Even though it cuts out after around two seconds, the commercial lasts long enough to show Marble Zone with the UFOs in the background!