Sonic & Knuckles

Sonic & Knuckles (Japanese: ソニック&ナックルズ, Hepburn: Sonikku to Nakkuruzu) is a 1994 platform video game developed by Sonic Team and published by Sega for the Sega Genesis/Mega Drive. Released on October 18, 1994, it was the fourth installment in the main Sonic the Hedgehog series. The game is a direct sequel to Sonic the Hedgehog 3, and follows both Sonic the Hedgehog and Knuckles the Echidna in their respective quests to save Angel Island; Sonic tries to prevent Dr. Robotnik from re-launching his orbital weapon, the Death Egg, while Knuckles scuffles with Robotnik's minion, EggRobo.

Sonic & Knuckles utilizes "lock-on technology" that allows the game to access data from both Sonic the Hedgehog 2 and Sonic the Hedgehog 3 so that elements of both Sonic & Knuckles and the locked-on game are combined. During the development of Sonic 3, it and Sonic & Knuckles were intended to be a single story within the same cartridge. However, due to time constraints and the fact that a large memory capacity cartridge would have been expensive, Sega split the game into two separate installments.