Sonic the Hedgehog 2
Console: Sega Genesis
Idea Change: Removal and repurposing of several stages
Complex Says: What if the Sonic Team had more cartridge space and time? Sonic 2 is already a classic, but imagine if they went with their initial ideas? If you grew up cycling through the music in the sound test, you may have come across a full Death Egg Zone song and a song that never appeared in the game. That unused song was for Hidden Palace Zone where Sonic would officially change into Super Sonic. Sound familiar? We'll get back to that.
If you scour YouTube for a glimpse of the stage, you'll fall into several stages that have been pulled from the game. Stages like Wood Zone, Genocide City Zone, Dust Hill Zone, and even Death Egg Zone were either scrapped or re purposed in the game. Game hackers found the backgrounds and layouts of these stages through debug mode and rom hacks and posted playthroughs of each zone including the unfinished, Hidden Palace Zone.
The idea for Hidden Palace Zone was later used in Sonic & Knuckles where you can face Knuckles and see where the emeralds you collect originated. Wood Zone was in an early build of the game along with Hidden Palace Zone before both stages were scrapped. Dust Hill Zone was scrapped from the game entirely as well as an act of Genocide City Zone. The remaining act of Genocide City was kept as Metropolis Zone act 3. Lastly, Death Egg Zone was cut down to just the boss act, while act 1 was used as Chemical Plant Zone act 1 since the stage was thought to be "too easy."