And Michael Jackson clearly wrote a lot of Sonic 3's music
There is so much evidence for this. The King of Pop loved video games, appeared in several Sega releases and (most obviously), several tunes in Sonic 3 sound exactly like sections of Michaels released tracks. Especially that bit in Carnival Night Zone. But then the unsavoury alligator unleashed his first round of unsavoury allegations and Jacksons involvement was totally shushed to distance Sega--and Sonic 3--from the scandal. A shame really. Sonic 3s soundtrack is amazing and credit is due.
Sonic & Knuckles' lock-on compatibility doesn't end with Sonic 2/3
When Sonic & Knuckles was first announced, it was supposed to add playable Knuckles to Sonic 3, Sonic 2 and even Sonic 1. But in the end, the levels in the original didnt suit him and the colour palettes were incompatible basically it didnt work. But if you simultaneously press A, B and C on the No way! screen, you can play Blue Sphere, a version of Sonic & Knuckles globe-based 3D special stage based on code from the locked-on game. How cool is that? Not all games work, but most early, 2MB ROM games (like Ecco The Dolphin) do. Crazy times.
Robotnik used to twerk. No, sorry, his wrecking ball was level furniture
And not only has it been seen in beta code, it can be accessed via the debug mode in the iOS/Android conversion of Sonic 1 by Christian Whitehead. Not only can the ball be pushed around the levels, it smashes through breakable walls and can even be dropped on Robotniks head in the boss fight, causing damage.
Incredibly, the physics engine not only allows multiple balls to roll around on the screen at once, they even collide with each other. Probably just Christian Whitehead having fun with his development toys, but it's amazing to see the ball working properly. It even smashes through breakable walls. I know I already said that, but it's amazing.
Sonic can't swim because Yuji Naka was mistaken
Yuji Naka thought that hedgehogs couldnt swim (they can), so Sonic just walks around underwater, breathing in gulps of air from cracks in the floor. Which is obviously much more believable.
Instruction manuals advertise items you cant ever collect through normal means
Sonic 1 shows an extra life icon in the bonus stage which is present, but only in an unfinished area outside of the normal level that you can only reach via the debug mode. Similarly, Game Gear Sonic 2s manual shows a pair of running boots in the first level but unlike the Master System version, you cant ever find them. Fail.
The Sonic 1 beta UFOs are present in an official release
Early footage of Sonic 1s pre-release phase (including Waynes World!) shows strange UFO-like objects in the Marble Zone sky. Theyre actually present in the debug mode of the iOS/Android version and can be called into play whenever you like. They dont do anything, although they are clearly a modern addition, as they feature transparency effects the Mega Drive wouldnt have been able to display.
Sonic was almost a rabbit
Early suggestions for Segas new mascot included a rabbit that grabbed enemies and items with its ears. But technical limitations at the time prevented that from being used for the Nintendo-beater. It is entirely likely that Ristar was born from this early concept, using his long arms to grab things and swing from them, once the Mega Drive tech was more understood.
Sonic 2 once contained a level called Genocide City
There are several levels in early betas for Sonic 2 that go by different names or were cut from the final product (in fact this level arguably never had any graphics, as this beta hack shows). One such stage was Genocide City. Likely an unfortunate misunderstanding of a literal translation, clearly this could never be the name for a family-friendly game. But Genocide City wasnt lost completely. Its single-act layout was reskinned... and became Metropolis Act 3. So thats why Metropolis is the only level to have 3 acts in Sonic 2. Its really Genocide City in disguise.
Sonic Adventure started life as a Saturn game
Sonic team made several prototypes on Saturn to see how Sonic would work in 3D, the best of which emerged as the Sonic 3D World section in Sonic Jam (pictured). But, having found a decent formula, the project was moved to Dreamcast as Saturn stalled and the new hardware loomed. I must say, though, Sonic Jams 3D Sonic controls exceptionally well. Maybe 3D Sonic should move at that kind of pace more often?
Sonic CD has a scary screen in it
Sonic CD has a scary screen in it with a weird-faced Sonic and Japanese text. Turned out to be a play on words (in Japanese) on the games Landscape Designer Masato Nishimuras name. The pun turns his name into another word for the devil, which is why some people thought this screen was put in the game by *cough* the devil. It wasnt--its just devilishly good. Hahaha.