An early illustration by Naoto Ōhshima featuring Sonic, Dr. Eggman, and Animals. This illustration was used to promote the game and was featured on various Sonic merchandise such as paper tags on Sonic plushes obtained through UFO Catcher machines.
An early sketch of Sonic that would later become used for the Japanese Box Art cover.
Concept of Sonic illustrating his run cycle and speed.
Concept of shuttle loop. Text Translation: "Metallic kind of stage... The background is styled like south-east Asia, golden country, (...) (are) gold colored plating."
Alternate scan of the shuttle loop art.
Concept of Green Hill Zone. Text Translation: "CG styled stage... Blue skies and green(ery) are the basis, nothing till now, CG styled background."
Original level map for Green Hill Zone.
Concept of unknown Zone. Text Translation: "Rocky mountain and underwater stage... Japanese styled rocky mountain stage, with underwater scene. In the map, spin (jump) and you can cross the water, but various techniques make it possible to (...) the course."
Alternate scan of the unknown Zone art.
Concept of Marble Zone. Text Translation: "Stage where the land shakes... The underground has an amoeba shape and the ground shakes. The amoeba shaped terrain (...) with canals. Can also dive into the ground."
Published in "SPEC," this concept art shares similar features to the early Green Hill Zone demonstration at the 1990 Tokyo Toy Show, including the trees, the mountains' blocy foundation, and Sonic's pose. It is unknown if this image was drawn by Naoto Ohshima.