Genocide City Zone

Genocide City Zone (AKA Cyber City Zone) was a scrapped level from Sonic the Hedgehog 2 for the Sega Mega Drive.

Description
The level was originally a concept for the Metropolis Zone act 3. In a prototype release dubbed "Simon Wai Prototype", the level was originally accessible, but lead to a room where Sonic would just fall to his death. Activating debug mode would cause the appearance of a ring and a teleport monitor. The music that was intended to be used for this level was used for Chemical Plant Zone instead.

In Sonic 2 Beta
When accessing Act 1 of the level in the Sonic 2 Beta, Sonic appears in a level with no objects. The background is blue with white lines and Sonic just falls to his death. There is not much known information on Act 2, but it is likely to be the same case. Sonic and Tails in Genocide City Zone can be seen at 0:47 in this video.