Sonic 3 & Knuckles is a fast-paced action game, which was made in 1994 by Sega. You can play either as Sonic, Tails, or Knuckles. The game consists of lots of running and jumping, destroying badniks and collecting Chaos Emeralds along the way. However, on the original Genesis/Mega Drive, there were two cartridges- Sonic 3, the main game, and Sonic & Knuckles. The second one listed here had a "lock-on" feature on the cartridge, meaning that you could insert Sonic 3 on the top of Sonic & Knuckles and play Sonic 3 & Knuckles. Sonic 3 and Sonic & Knuckles are therefore two completely different games.