Genocide City Zone is a scrapped level from Sonic the Hedgehog 2. It was meant to be a single level which used the map that ultimately became Metropolis Zone Act 3. Concept art of it has been Reticon.pngreleased revealing that the level's name was originally Cyber City. Due to the level being mechanically themed, instead of grim and deadly as the name implied, the theory that this magazine clip referenced the boss of Genocide City seems unlikely.
It is listed in the level select menu in the Simon Wai prototype but selecting it simply brings the player to a empty level. Chemical Plant Zone music plays with Emerald Hill's palette (discovered in Esreal Sonic Editor), and the player will simply fall to their death at the bottom of the stage. Enabling debug reveals that the only objects in this level are the two default objects, a ring and a teleport monitor.
According to Sonic 2 level designer Tom Payne, the name "Genocide City" being chosen was due to the development team's "not quite complete grasp of the English language." During an interview with Payne, he went on to say that the team "may have been looking for a name that sounded dangerous," which resulted in the name "Genocide City" appearing in one of the Sonic 2 betas. It is now believed that Cyber City was the name conceptualized later on in order to remedy the zone's former name.
According to ICEknight, Tom Payne used the theme of the level to create some graphics for an unreleased game called B-Bomb. He then used them in the Sonic Spinball level, The Machine.