This Subpage is for the Sonic and Knuckles Lock-on.
Sonic 3 & Knuckles Edit
The most famous expansion of the add-on. What this basically does, is that it expands the game beyond Launch Base Zone, allows Knuckles to be playable, fixes the level select to use the Sonic and Knuckles version, and replaces the Title Screen, invisablity, Act 1 boss and Knuckles themes with the Sonic and Knuckles versions.
Knuckles in Sonic 2 Edit
If locked on to Sonic 2, the game will allow Knuckles to be playable in Sonic 2.
Blue Sphere Edit
if Locked on Sonic 1, or the Nick Arcade and Simon Wai Prototypes of Sonic 2. The game will launch a "mini-game" called "Blue Sphere", which is the bonus stage of Sonic 3. Originally, there would have been a "Knuckles in Sonic 1", although due to technical issues during development, it was replaced with Blue Sphere.