The following is a list of version differences between the various ports of Sonic the Hedgehog 3, Sonic & Knuckles and Sonic 3 & Knuckles. Throughout the various releases, it has been subject to alterations of the gameplay and certain mechanics. Some versions also have various new additions not present in the original release.
Due to the nature of their development and original intent as seen. For Sonic's Ultimate Genesis Collection on the Xbox 360, a GameFAQs message board topic titled "What's the difference between sonic 3 and knuckles and sonic and knuckles?". Most importantly, code in Sonic & Knuckles finishes the Sonic 3 routes intended for Knuckles.
From the very beginning, Sonic 3 stages were designed with Knuckles-only areas (visible in that game through edit mode), but progress was put on hold when the game was split in two. Differences between S3 and S3&K Only Sonic and Tails are playable. The Title Screen theme, Knuckles theme, Invincibility theme, Ending theme, and the Act 1 Boss theme were changed in S3&K Sonic can only fight the 2nd phase of the Launch Base Zone act 2 boss in S3.
Launch base zone is much harder in S3 due to it being the final zone in that game. Why was Sonic 3 and Knuckles split? Sonic the Hedgehog 3 and Sonic & Knuckles were planned as single game, but were released separately due to time constraints and cartridge size limitations. The Sonic & Knuckles cartridge features a "lock-on" adapter that allows other Genesis cartridges to be attached.
Originally, Sonic 3 and Sonic & Knuckles were intended to be released as a single game, but time constraints and hardware limitations resulted in this game being split into two separate titles. [3] Sonic 3 & Knuckles is the combined story of Sonic 3 and Sonic & Knuckles, first starting with the former's stages and continuing with the latter. In this little topic me and Zenon wanted to point out some of the differences between Sonic the Hedgehog 3 and Sonic 3 & Knuckles.
It seems like it's the same game, what's the point? But S3&K was some kind of a "fix" of Sonic 3. And it made the differences apear. Some glitches were fixed.
The differences between Sonic 3 and Sonic 3 & Knuckles are a few things, the first being able to play as the Echidna in the Sonic 3 section of the game (Angel Island - Launch Base) and to be able to play as Tails in the S&K section of the game (Mushroom Hill - Death Egg). The beauty of "Sonic 3 & Knuckles" is the ability to play as Knuckles throughout the entire combined game. Knuckles's story is essentially the same as Sonic's, but with significant differences.
Knuckles' levels are different from Sonic's and Tails' in most cases, with new areas and bosses. There are slight differences in object placement in some of the Sonic 3 Zones (Launch Base especially). Sonic and Tails skips the final boss of Launch Base, while Knuckles still has to do it (although he skips the first true boss of Launch Base).