The first showing of Sonic the Hedgehog in video game form was at the Tokyo Toy Show in June 18, 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 first known build has some advantages over 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 mainstream product.
Allegedly, this demo was planned to be included in Sonic Mega Collection, but was never in any build as the ROM has since been lost internally at Sega.