The player character moves through six levels, each divided into two acts. There is also no multiplayer mode or save feature. However, in Sonic & Knuckles, unlike in Sonic 3, the player chooses either Sonic or Knuckles at the title screen, Miles "Tails" Prower is not available to select, and the player cannot control two characters together.
Since Sonic & Knuckles and Sonic the Hedgehog 3 were initially developed as one game, their gameplay is similar: both are 2D side-scrolling platformers with similar level design, graphics, and game mechanics. Knuckles explores Mushroom Hill, the first zone of Sonic & Knuckles.
They have since been rereleased in various Sega and Sonic compilations. The games sold a combined four million copies worldwide, placing them among the best-selling Sega Genesis games. It received positive reviews critics were impressed with the replay value and lock-on technology, despite its similarity to Sonic 3. Sonic & Knuckles was released for the Sega Genesis on October 18, 1994. Attaching the original Sonic the Hedgehog or any other Genesis game released prior to this will unlock the "Blue Sphere" minigame. Sonic the Hedgehog 2 (1992) can also be attached, allowing players to control Knuckles in Sonic 2 stages. The Sonic & Knuckles cartridge features an adapter that allows players to connect the Sonic the Hedgehog 3 cartridge, creating a combined game, Sonic 3 & Knuckles. Sega Technical Institute developed Sonic & Knuckles simultaneously alongside its predecessor, Sonic the Hedgehog 3 (1994) they were planned as a single game until time constraints and cartridge costs forced the developers to split it. Like previous Sonic games, players traverse side-scrolling levels at high speeds while collecting rings and defeating enemies.
Players control Sonic the Hedgehog and Knuckles the Echidna in their quests to save Angel Island Sonic tries to prevent Doctor Robotnik from relaunching his orbital weapon, the Death Egg, while Knuckles scuffles with Robotnik's minion, EggRobo. Sonic & Knuckles is a 1994 platform game developed and published by Sega.