Sonic & Knuckles is the fourth Sonic game in the series (not including Sonic Spinball etc.) and is the first game where you can play Knuckles. You can choose to play as Sonic and Knuckles, and each has a route through the levels. Also, Knuckles can only go up to Sky Sanctuary, where Sonic can go to Doomsday Zone (if he has all 7 emeralds). This game plays very much like Sonic 3, because it was intended to be a part of Sonic 3 but they couldn't fit all the levels into one cartridge so they divided the game into two, Sonic 3 and Sonic & Knuckles. Sonic & Knuckles has a special lock-on which lets you play Sonic 2 as Knuckles to find the hidden stuff that you can't get as Sonic or Tails, or lock on Sonic 3 to play the full game, with a choice of playing as Sonic, Tails, Knuckles or Sonic and Tails together.
Sonic & Knuckles Levels
