Sonic & Knuckles + Sonic 2

Sonic & Knuckles is a 1994 platform video game in the Sonic the Hedgehog series for the Sega Mega Drive/Genesis. It was developed in the United States at Sega Technical Institute by members of Sonic Team, and was published by Sega worldwide on October 18, 1994.

In addition to being a standalone game, through a system dubbed "lock-on technology," Sonic & Knuckles acts as an expansion pack to both Sonic the Hedgehog 2 and Sonic the Hedgehog 3, the latter with which it was developed in tandem.

Because Sonic & Knuckles and Sonic the Hedgehog 3 were originally going to be one game, gameplay is nearly identical to Sonic 3. The game still plays as a 2D sidescrolling platformer, with the player directing Sonic through levels and around obstacles within a time limit of 10 minutes. However, while Tails is no longer a playable character, the game does introduce Knuckles the Echidna as a playable character.

Gameplay slightly differs between playing as Sonic or Knuckles. Sonic is able to run faster and jump higher than Knuckles, and can also utilize the special abilities of elemental shields. Meanwhile, Knuckles has the ability to glide through the air, climb up walls, and break through certain barriers, all allowing him to access new areas Sonic cannot. Knuckles' route consists of fewer levels, but more complicated level layouts.[citation needed]

The game has 2 bonus mini-games that can be accessed by hitting checkpoints with 20 or more rings and jumping through the stars. The first involves players attempting to earn rings in slot machines, where the other type sees the player traveling upwards through the use of magnetic orbs and flippers, collecting rings while avoiding a slowly rising forcefield that ends the mini-game.

The "special stages", the method in which Sonic collects the Chaos Emeralds in the game, play exactly like they do in Sonic 3, except with different layouts