Sonic & Knuckles is a 2D action platformer developed by Sonic Team (with assistance from Sega Technical Institute) and published by Sega for the Sega Genesis on October 18, 1994. The direct sequel to Sonic the Hedgehog 3, Sonic & Knuckles continues the story of Sonic the Hedgehog, who must venture deeper through Angel Island to track down Dr. Robotnik (whose orbital weapon, the Death Egg, crashed back down to the floating island during the events of Sonic the Hedgehog 3), while still being pursued by Knuckles the Echidna (who still believes Sonic is stealing the island's Chaos Emeralds).
Players can also play as Knuckles himself through the game (previously only playable in Sonic the Hedgehog 3's Competition Mode), in which he runs slower and jumps lower than Sonic (and cannot use the special abilities of elemental shields), but has the unique abilities to glide through the air, climb walls, and punch out certain obstacles (as well as having to face more difficult boss battles as an added challenge). He has his own side-story, taking place after the main campaign, in which a surviving badnik (the EggRobo) takes Dr. Robotnik's place in finding the Master Emerald (though it is not sure, until the end of the game, who the main antagonist is).
Sonic & Knuckles is the last Sonic game to be worked on by Sega Technical Institute. The soundtrack was composed by STI's Howard Drossin.
In Sonic & Knuckles, players control either Sonic the Hedgehog or Knuckles the Echidna as they navigate through 6-8 levels (known as "Zones", split into different "Acts") to track down Dr. Robotnik (in Sonic's campaign) or the lone EggRobo (in Knuckles's campaign). Players must dodge dangerous obstacles (such as spikes and bottomless pits) and plow through enemies (with attacks such as the rolling jump) to reach the end of each Act.
Like Sonic the Hedgehog 3, each main level (known as Zones) are split into two unique sections (known as Acts), each act with a unique setting (such as Sandopolis Zone starting out in the vast desert and ending up inside a haunted pyramid) and music. The first act ends with one or more mini-bosses to fight and the second act ends with a boss to fight.
Hidden Palace Zone and Sky Sanctuary Zone have only one "act" and both serve as two "acts" to one "level". Both are heavily shortened and modified for Knuckles's campaign (the first as a simple transition and the second as the Knuckles's final boss battle). Death Egg Zone and Doomsday Zone cannot be played as Knuckles. Doomsday Zone can only be played as Super Sonic (or Hyper Sonic in Sonic 3 & Knuckles) and has only one "act", serving as the Sonic's final boss battle.
In Sonic 3 & Knuckles, all of the Sonic & Knuckles levels appear immediately after all of the Sonic the Hedgehog 3 levels.
- Mushroom Hill Zone
- Flying Battery Zone
- Sandopolis Zone
- Lava Reef Zone
- Hidden Palace Zone
- Sky Sanctuary Zone
- Death Egg Zone (Sonic Only)
- Doomsday Zone (Super/Hyper Sonic Only)
The game utilizes "lock-on technology" (in which the unique game cartridge features its own Sega Genesis cartridge slot at the top), so that the cartridge can access data from other Genesis games. Booting up the game without any cartridge locked-on plays Sonic & Knuckles normally. With most cartridges locked-on, the game shows up a special "No Way!" screen (in which players can play a secret random pre-generated Special Stage by pressing all buttons simultaneously). For the three main Sonic the Hedgehog games:
With Sonic the Hedgehog locked-on, one of the message changes to "No Way?" and pressing all buttons simultaneously unlocks a deeper Special Stage game (known as "Get Blue Spheres!" or, retroactively as "Blue Sphere"). Players can play a series of pre-generated Special Stage levels (up to 134,217,728 configurations of varying difficulty) and keep track of their progress using a 12-digit numerical password.
Earning a "Perfect" in the stage (by collecting all possible rings) skips ahead 10 stages. Players start at level 1 and can change the password before entering the stage (including passwords given out after completing a Special Stage with any other cartridge). There were plans to make Knuckles playable in Sonic the Hedgehog, but the concept was later scrapped.
Knuckles the Echidna in Sonic the Hedgehog 2
With Sonic the Hedgehog 2 locked-on, players can play Knuckles the Echidna in Sonic the Hedgehog 2, in which they can play through the entirety of Sonic the Hedgehog 2 as Knuckles. Knuckles retains all of his abilities (and flaws), and the game adds some new hidden items (that makes use of Knuckles's abilities). Two-player mode (including Time Trials mode) is disabled.
Sonic 3 & Knuckles
With Sonic the Hedgehog 3 locked-on, players can play Sonic 3 & Knuckles, which combines both games into one "complete" game (with the Sonic the Hedgehog 3 campaign leading to the Sonic & Knuckles campaign). With this setup, players can play the Sonic the Hedgehog 3 campaign as Knuckles (complete with branching paths, due to his abilities, and a harder EggRobo boss at the end of each zone), play through the Sonic & Knuckles campaign as Tails (or as Sonic with Tails), and save their progress in the Sonic & Knuckles campaign (complete with more save slots).
In addition, players who reach the Sonic & Knuckles campaign with all seven Chaos Emeralds can trade them for the ability to collect seven Super Emeralds (Chaos Emeralds powered-up by the Master Emerald). When they have all seven Super Emeralds, they can transform into Hyper Sonic (who, in addition to the abilities as Super Sonic, gains the ability to perform a mid-air dash that flashes the screen, clearing all enemies on the screen), Hyper Knuckles (who, in addition to the abilities as Super Knuckles, triggers a earthquake when clinging on to a wall, clearing all enemies on the screen), or Super Tails (who has the abilities of Super Sonic as well as being surrounded by four super-powered Flickies that automatically charge at enemies on the screen).
Ports and Compilations
The game was later ported (alongside Sonic the Hedgehog 3) by Sega to PC (running Windows 95 and up) as Sonic & Knuckles Collection (published by Sega for Japan in 1997 and Expert for North America in 1999). The game retains the same gameplay as the Sega Genesis version, but the music was re-done in MIDI format. It also includes the option to play Sonic 3 & Knuckles (both games locked-on, see "Lock-On Technology") and also includes a Sonic-themed screensaver.
Sega compilations that include both Sonic & Knuckles and all of its lock-on functionality (as separate modes) include Sonic Jam (on July 31, 1997 for the Saturn), Sonic Mega Collection (on November 10, 2002 for the GameCube), and Sonic Mega Collection Plus (for the PlayStation 2 and Xbox on November 2, 2004 and for the PC on March 9, 2007). Sonic's Ultimate Genesis Collection (for the Xbox 360 and PlayStation 3 on February 10, 2009) includes the game but none of the lock-on functionality. Sonic Classics Collection (for the Nintendo DS on March 2, 2010 in Europe only) includes the game and both the Sonic the Hedgehog 2 and Sonic the Hedgehog 3 functionality.
The game has been ported and digitally released on the Wii (via Wii Virtual Console on September 9, 2009) and Xbox 360 (via Xbox Live Arcade on February 15, 2010). Both releases are programmed so that if the owner has downloaded this and any of the three Sonic games originally required for lock-on functionality, he/she can play that Sonic game as if it was going through the Sonic & Knuckles lock-on technology.