Sonic the Hedgehog (lost Tokyo Toy Show prototype build of Sega Genesis/Mega Drive platformer; 1990)
The first showing of the 1991 Sega Mega Drive game Sonic the Hedgehog was at the Tokyo Toy Show in June 1990, which also happened to be the first time the game could be played by the public. In an interview with Yuji Naka, it was revealed that the original Sonic Team put together a small, playable technical demo for the show featuring Sonic in an early version of the Green Hill Zone. Though development had just begun, this build was actually more technically advanced than the final version of the game, possessing seven layers of parallax scrolling, with trees and rocks in the foreground being independent from the clouds and other objects in the background, all separate from the scrolling of Sonic the Hedgehog as he ran through the hilled terrain.
Being the earliest representation of the Green Hill Zone, it is also reflective of what was found in early materials used both internally and in promotional articles. One of the most noticeable differences between this version and the final are the strange blue structures in the background, though it is unknown if they are meant to represent a city or are simply a natural yet surreal rock formation. With both trees and giant rocks in the foreground (which presumably had layers of scrolling independent of each other), the entire style was indicative of what was to come. Though foreground items were not found in the final, the rocks would be modified and used in the released layouts of the game, transformed into downsized, colored purple obstacles in the final release. The clouds of this early pre-release are also bigger, seemingly appearing with less frequency than in the final product.
The demo has not been released or leaked in any way. In the same Game Radar interview with Yuji Naka, Naka reveals that the prototype was planned to be included in Sonic Mega Collection (A compilation of all Sonic the Hedgehog games for the Sega Mega Drive, released for the Nintendo GameCube in 2002), but was never put in due to Sega losing the ROM, making it highly unlikely the demo will ever be released.