There are several noticeable differences when playing the games combined. In Sonic Classic Collection, for unknown reasons, the game was renamed to Knuckles in Sonic 3. It acts as one large combined game and all the levels from Sonic 3 and Sonic & Knuckles become available. Sonic 3 & Knuckles is a game that results when Sonic 3 is locked-on to Sonic & Knuckles via Lock-On Technology.
