When Sonic 3 is inserted, the player can play through both games as one, Sonic 3 & Knuckles. Sonic & Knuckles features "lock-on technology" that allows players to open the hatch on the cartridge and insert a second cartridge. Completing a Special Stage earns the player a Chaos Emerald collecting all seven Emeralds allows the player to turn into Super Sonic or Super Knuckles, more powerful versions of the characters. Yellow spheres bounce the player long distances, and white spheres with red stars on them make the player walk backwards in the opposite direction. Special Stages are entered by finding giant rings hidden in secret passageways: the player is placed in a 3D environment and must turn all of a number of blue spheres red by running through them, but must avoid all red spheres, including formerly blue ones. The second type involves bouncing around a room with a slot machine in its center with the intention of winning extra lives and power-ups. Collecting 50 rings in this stage earns the player a continue. The first type has Sonic or Knuckles orbit floating, glowing spheres, jetting off each one when a button is pressed, while a fence of light approaches from the bottom and will remove the player from the stage if touched. The game contains two types of bonus stages accessed by passing a checkpoint with at least 20 rings. The levels also include cutscenes that differ based on the character selected, as Sonic and Knuckles are opponents for most of the game. Sonic and Knuckles traverse levels differently Sonic can jump slightly higher and has access to unique shield abilities, whereas Knuckles can glide and climb most walls. Robotnik's robots, while the second ends with a regular boss fight with Robotnik (or EggRobo in Knuckles' campaign). The first act of each level ends with a miniboss fight with one of Dr. 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 It has also been re-released through various compilations and on digital platforms such as Xbox Live Arcade and the Wii's Virtual Console, while it was bundled with Sonic 3 on Steam.
Alongside Sonic 3, a Windows port was released through the Sonic & Knuckles Collection (1997). Sonic & Knuckles received positive reviews critics were impressed with the replay value and lock-on technology, despite its similarity to Sonic 3. Sonic 3 & Knuckles sold a combined four million copies worldwide, making them some of the best-selling Sega Genesis games. Sonic & Knuckles was released for the Sega Genesis on October 18, 1994. 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 Sonic 3 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. The sequel to Sonic the Hedgehog 3 (1994), 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 video game developed and published by Sega.