Sonic & Knuckles was developed by the Sega Technical Institute in collaboration with Sonic Team, and published by Sega for the Genesis/Mega Drive in 1994. It is the direct sequel to Sonic 3, which was released earlier that year and it seems that some removed levels from S3 were later re-used for S&K. As our friends at X-Cult say: “Sonic & Knuckles is, at it’s heart, a continuation of Sonic 3; or rather, a collection of Sonic 3’s lost levels and then some”. It seems that the project was originally named “Sonic 3 & Knuckles”
In these beta images we can see an unknown “carnival night zone” and the Sonic 2 “Hidden Palace” in the hacked level-select menu screen, while in the other gameplay ones there are probably just graphical differences that are minor.
Also, Interesting fact to note. Sonic 3 and Knuckles Developer Roger Hector points out that Sonic 3 and Knuckles was going to be an isometric 3D style game in a similar fashion to sonic 3D blast. Also, it was confirmed that Micheal Jackson did work on the game’s soundtrack. The soundtrack was re-written by Howard Drossin due to the development team removing Jackson’s soundtrack cause of a child molestation scandal near the end of the game’s development cycle.