Sonic & Knuckles is a 1994 platform game created by Sega Technical Institute and released by Sega for the Sega Genesis. Players can control Sonic the Hedgehog or Knuckles the Echidna as they work to save Angel Island. Sonic aims to stop Doctor Robotnik from launching his orbital weapon, the Death Egg, while Knuckles fights Robotnik’s robot, EggRobo. Like earlier Sonic games, players move quickly through side-scrolling levels, collect rings, and defeat enemies.

Sega Technical Institute made Sonic & Knuckles at the same time as its earlier game, Sonic the Hedgehog 3 (1994). Originally, the two games were planned as one, but time limits and costs forced the developers to separate them. The Sonic & Knuckles game cartridge includes an adapter that lets players attach the Sonic the Hedgehog 3 cartridge, combining the two into a single game called Sonic 3 & Knuckles. The Sonic the Hedgehog 2 (1992) cartridge can also be attached, allowing players to control Knuckles in Sonic 2 levels. Adding the original Sonic the Hedgehog or any earlier Genesis game unlocks a minigame called "Blue Sphere."

Sonic & Knuckles was released for the Sega Genesis on October 18, 1994. It received positive reviews, with critics praising its replay value and lock-on technology, even though it was similar to Sonic 3. Together, Sonic 3 and Sonic & Knuckles sold four million copies worldwide, making them some of the best-selling Sega Genesis games. They have been re-released in several Sega and Sonic compilations.

Gameplay

Sonic & Knuckles and Sonic the Hedgehog 3 were created as one game, so they share similar gameplay. Both are 2D side-scrolling platformers with similar levels, graphics, and rules. In Sonic & Knuckles, players choose either Sonic or Knuckles at the start, but cannot select Miles "Tails" Prower or control two characters together. There is no multiplayer mode or save feature.

The player moves through six levels, each split into two acts. The first act ends with a fight against a miniboss, while the second ends with a boss fight against Dr. Robotnik (or EggRobo in Knuckles’s story). Sonic and Knuckles move differently: Sonic jumps higher and has shield abilities, while Knuckles can glide and climb walls. Cutscenes change depending on which character is chosen, as Sonic and Knuckles are enemies for most of the game.

Two bonus stages can be entered by collecting 20 rings at a checkpoint. The first stage involves orbiting glowing spheres and avoiding a light fence. Collecting 50 rings here gives a continue. The second stage involves bouncing around a room with a slot machine to earn extra lives and power-ups.

Special Stages are entered by finding hidden giant rings. Players enter a 3D environment and must turn blue spheres red by running through them while avoiding red ones. Yellow spheres launch the player far, and white spheres with red stars make the player move backward. Completing a Special Stage gives a Chaos Emerald. Collecting all seven emeralds allows the player to transform into Super Sonic or Super Knuckles, stronger versions of the characters.

The game includes "lock-on technology," allowing players to insert a second cartridge. Combining Sonic 3 with Sonic & Knuckles creates a merged game, Sonic 3 & Knuckles, with altered levels, the ability to play as Tails, and a save feature. This combination also allows collecting "Super Emeralds" by completing Special Stages in Sonic & Knuckles after collecting all Chaos Emeralds from Sonic 3. Collecting all Super Emeralds lets Sonic, Knuckles, and Tails transform into Hyper Sonic, Hyper Knuckles, and Super Tails, each with unique abilities.

Inserting Sonic 2 into the cartridge unlocks Knuckles in Sonic the Hedgehog 2, allowing players to use Knuckles’s abilities in that game. Attaching other Genesis games before Sonic & Knuckles shows a screen with Sonic, Tails, Knuckles, and Robotnik saying "No Way!" and includes a minigame based on Chaos Emerald stages. The attached cartridge determines the stage layout. Using the original Sonic the Hedgehog allows access to all special stage variations, each with a unique number and password. This game is called "Blue Sphere" in Sonic Mega Collection and "Blue Spheres" in Sonic Origins.

Plot

After the events of Sonic 3, Dr. Robotnik’s space weapon, the Death Egg, crashes onto Angel Island. Sonic travels to Angel Island to find the Chaos Emeralds to stop Robotnik. He faces Knuckles again, who believes Sonic wants to take the Emeralds for himself. In Hidden Palace Zone, Sonic defeats Knuckles and learns that Robotnik is stealing the Master Emerald, a gem that gives Angel Island its ability to float. Knuckles tries to stop Robotnik but is shocked by electricity. Knuckles shows Sonic a portal that leads to Sky Sanctuary, where the Death Egg is being launched again. Sonic enters the Death Egg, defeats Robotnik as Super Sonic, retrieves the Master Emerald, and returns it to Angel Island, which rises back into the sky.

In Knuckles’s story, which happens after Sonic’s, Knuckles is attacked by EggRobo, one of Robotnik’s robots. He follows EggRobo to the broken parts of Sky Sanctuary, where Mecha Sonic attacks Knuckles. Mecha Sonic accidentally destroys EggRobo instead. Mecha Sonic uses the Master Emerald’s power to become a strong form like Sonic’s and fights Knuckles. Knuckles eventually defeats Mecha Sonic. Sonic arrives in a plane called the Tornado and takes Knuckles and the Master Emerald back to Angel Island. If all the Chaos Emeralds are collected, Angel Island rises into the sky. If not, Angel Island falls into the ocean.

Development

Sonic & Knuckles was created in California by Japanese members of the Sega Technical Institute (STI). Sonic 3 and Sonic & Knuckles were first planned as one game. Designer Takashi Iizuka said the team wanted to create a very successful game with larger levels that took more time to make. Because ROM cartridges were too small to hold the full game and Sega needed to release it in time for a promotional deal with McDonald's in the United States, the game was split into two parts. Sonic & Knuckles became the second part, and its first level, Mushroom Hill, was made easier to play.

Although the games were split, the developers wanted players to feel like they were playing one continuous experience. Roger Hector, vice president and general manager of STI, said the lock-on technology was created between the releases of Sonic the Hedgehog (1991) and Sonic the Hedgehog 2 (1992).

The team shared their situation with Sega's hardware division, which provided them with a lock-on adapter. Knowing players might use the adapter to play other games alongside Sonic 3, the team added the Blue Sphere minigame to most games. They also made Knuckles playable in Sonic 2 if that game was inserted, because his play style matched the levels. The team considered adding this feature to the original Sonic the Hedgehog, but decided Knuckles's abilities did not fit the level design of that game.

Release

Sonic & Knuckles was released on October 18, 1994. Around the same time, Nintendo released Donkey Kong Country for the Super Nintendo Entertainment System, which was a competitor to the Genesis. Industry experts referred to the simultaneous releases as a "battle," as both games advertised "revolutionary" technological advances: lock-on technology for Sonic & Knuckles and 3D-rendered graphics for Donkey Kong Country.

Sonic & Knuckles was supported by a $45 million marketing campaign. At the time, video games usually had a marketing budget of $5 million. Blockbuster Video and MTV helped sponsor a tournament where children could play Sonic & Knuckles. The final event was held at Alcatraz Island in San Francisco, California, with a prize of $25,000 and the title "The World's Most Hardcore Gamer." Two finalists also received a copy of every Sega product released in the following year. MTV broadcast the tournament finale and footage of the game as part of MTV's Rock the Rock.

Rereleases

Sonic & Knuckles has been included in many collections of Sega games. These include Sonic Jam (1997) for the Sega Saturn, Sonic & Knuckles Collection (1997) and Sonic & Garfield Pack (1999) for the PC, Sonic Mega Collection (2002) for the GameCube, Sonic Mega Collection Plus (2004) for the PlayStation 2, Xbox, and PC, Sonic's Ultimate Genesis Collection (2009) for the Xbox 360 and PlayStation 3, and Sonic Classic Collection (2010) for the Nintendo DS.

Sonic Jam included the original game and added new ways to play: "Normal" mode changed the placement of rings and obstacles, and "Easy" mode removed some levels. The version in Sonic's Ultimate Genesis Collection did not include the "lock-on" feature found in other versions because of limited time for development.

The game was later re-released on the Wii's Virtual Console and the Xbox 360's Xbox Live Arcade. If a player downloads any "Lock-on" games on the same account, they can access connected versions of the game. For example, if a player downloads Sonic & Knuckles and Sonic 2, they can play the Knuckles version in Sonic 2. When the PC version was released through Steam, Sonic 3 & Knuckles was released as one game, allowing players to continue from the start of Sonic & Knuckles after finishing Sonic 3, even if playing as Tails.

Sonic & Knuckles is part of the Sega Genesis Flashback console, released in 2017 by AtGames. This console includes 45 Genesis games, but it does not include Sonic 3.

Sonic 3 & Knuckles was re-released for the first time since 2011 in 2022 as part of the Sonic Origins collection. All games in Origins are remastered versions using the Retro Engine. Sonic 1, 2, and CD are new ports of previously remastered games. This version was created by Simon Thomley of Headcannon, who also worked on Sonic Mania and other titles in the collection. The Origins version includes the original "Blue Sphere" minigame as a bonus and a new version called "New Blue Spheres," which adds colors from Sonic Mania.

Reception

The Genesis version sold at least 1.24 million copies in the United States. Sonic 3 and Sonic & Knuckles sold a combined total of 4 million cartridges worldwide.

Critics praised Sonic & Knuckles, even though it was similar to its predecessor. Four reviewers from Electronic Gaming Monthly named it their "Game of the Month." They praised the lock-on technology and noted that although the game was "more of the same," it was still an exceptional game. GamePro said the ability to play as Knuckles made the game feel like two separate games on one cartridge. They also stated the game was more challenging than Sonic 3 and that connecting the cartridge to Sonic 2 and 3 made those games "worth playing again." GamePro gave it a perfect score of 5.0 out of 5 in all four categories: graphics, sound, control, and fun factor. Next Generation remarked, "This is the same Sonic game that Sega has sold for the last three years, just wrapped up better and with a prettier ribbon."

Critics praised the lock-on technology the game offered. Lucas Thomas of IGN said it was "a great game on its own," but the lock-on feature completely changed the overall experience. Dan Whitehead of Eurogamer preferred Sonic & Knuckles to Sonic 3, saying he could not fully appreciate its predecessor without its "companion piece." Sega Power’s review praised the game’s harder difficulty compared to its predecessor and the new expansion of levels. It noted that the expansion would not have been possible if Sonic 3 had been a single game. Sega Magazine’s review also praised the lock-on technology and the new innovation of the unique cartridge. It added that Sonic & Knuckles’ hidden stages and bosses would increase the replay value of the combined game.

Reviewing the Virtual Console release, Nintendo Life writer James Newton praised the support for the original lock-on feature, saying the game does not truly shine without purchasing Sonic the Hedgehog 2 and 3 to activate this feature. Thomas praised the game for "impressive visuals that pushed the Genesis to its limits" and for the value added through content unlocked by the lock-on technology.

Legacy

In 2011, to celebrate the series' 20th anniversary, Sega released Sonic Generations, a game that included parts from older games in the franchise. A version of the Sky Sanctuary stage was included in the Xbox 360, PlayStation 3, and PC editions of the game, while the Mushroom Hill level was included in the Nintendo 3DS version. The game Sonic & Sega All-Stars Racing featured a track based on the Death Egg as extra content, along with the character Metal Sonic. Its sequel, Sonic & All-Stars Racing Transformed, included the same track and added another one inspired by the Sky Sanctuary stage. The 2017 game Sonic Mania included redesigned versions of the Flying Battery and Lava Reef stages, as well as the Blue Sphere bonus game. Sonic the Hedgehog 2 was influenced by Sonic & Knuckles, though it was not a direct copy.

In 2022, 30 years after the original game's release, Paramount announced the movie Sonic the Hedgehog 3 would be released in December 2024, and the show Knuckles would premiere on Paramount+ in April 2024. The creative team behind the live-action series confirmed this was meant to honor the original Sonic the Hedgehog 3 and Sonic & Knuckles double-feature release.