There was originally a stage called Hidden Palace Zone in the game. It featured an underground cave full of shiny gems. Code for the stage exists on the final version of the cartridge, however it cannot be played through normal means. In an interview, Yuji Naka revealed that the player would be warped to the Hidden Palace Zone when all 7 Chaos Emeralds were collected. There, you would be given the ability to become Super Sonic.

Early versions of the stage can be played in prototypes of the game.