Sonic the Hedgehog 3 & Knuckles

Sonic the Hedgehog 3 & Knuckles (or simply Sonic 3 & Knuckles or Sonic 3 Complete Version ) is a platformer video game which is the result of locking-on Sonic & Knuckles with Sonic the Hedgehog 3 using the former catridge's unique "Lock-On" technology. The game essentially is a large combined game of its two lock-on components and contains all Zones from the said games. This would have been the original Sonic the Hedgehog 3 but time constraints by Sega resulted in the game being split into two.

Gameplay

 * Further reading: Sonic the Hedgehog 3 and Sonic & Knuckles

Changes
While the gameplay in Sonic 3 & Knuckles generally remains identical to its two components, there are a large number of gameplay changes present, including:


 * The player can play as Knuckles in the Sonic the Hedgehog 3 levels although Knuckles' opening cutscene from Sonic & Knuckles has been removed.
 * As such, Knuckles' levels are different from Sonic's and Tails' in most cases, with new areas and bosses that are generally more challenging or different (in the case of Launch Base Zone) than Sonic/Tails' bosses.
 * The player can play as Tails in the Sonic & Knuckles levels (except for The Doomsday Zone) or have Tails follow Sonic throughout the entire game.
 * After the levels of Sonic the Hedgehog 3 are finished, the screen scrolls downward with the Death Egg rather than playing the normal ending animation, and gameplay immediately proceeds to the levels of Sonic & Knuckles. The final boss of Sonic the Hedgehog 3 is also omitted for Sonic and Tails.
 * Game progress can be saved in Sonic & Knuckles using the save feature of Sonic the Hedgehog 3 (there are now 8 rather than 6 save slots). In addition, any existing save files from Sonic the Hedgehog 3 will transfer to Sonic the Hedgehog 3 & Knuckles; ie. a game completed in Sonic the Hedgehog 3 will act as a Mushroom Hill Zone save file (this feature is missing in some later compilations).
 * Save slots now display information about the number of continues, lives and the Chaos Emeralds surround the player's character as the player collects them (the Chaos Emeralds are replaced with their correspondingly colored Super Emeralds when the player collects them). Save files imported from Sonic the Hedgehog 3 will retain the character, last zone and number of Emeralds, but will default to three lives and zero continues.
 * The game uses the sound bank of Sonic & Knuckles exclusively, which means that the BGM tracks that were different between Sonic the Hedgehog 3 and Sonic & Knuckles (which include the title screen, 1-Up, Invincibility, Act 1 boss music, Knuckles' theme and end credits theme) use only the Sonic & Knuckles version.
 * All Act title cards now display the game title of Sonic 3 & Knuckles.
 * Passing a Star Post can now open up all 3 Bonus Stages, including the slot machine stage (20-34 rings required), the magnetic orbs stage (35–49 rings required) from Sonic & Knuckles as well as the gumball machine (50–65 rings required) from Sonic the Hedgehog 3.
 * There are slight differences in object and enemy placement in some of the Sonic 3 Zones as well (Launch Base Zone in particular).
 * The method of accessing Sound Test/Act Select and Debug Mode is different.
 * With Debug Mode enabled, the player can access any level with any character, even those that cannot be normally accessed (such as Sonic and/or Tails accessing Knuckles' Sky Sanctuary Zone, Knuckles accessing Death Egg Zone or even Tails or Knuckles accessing The Doomsday Zone).

Super Emeralds
Collecting all the Chaos Emeralds in the levels of Sonic the Hedgehog 3 will turn Sonic or Knuckles into Super Sonic or Super Knuckles. However, once the player enters their first Special Stage in Mushroom Hill Zone, they teleport to Hidden Palace Zone where the Emeralds are taken from them and transformed into gray (apparently depleted of power) Super Emeralds, thus beginning the Super Emerald quest. If the player does not have all of the Chaos Emeralds prior to reaching Mushroom Hill Zone, the acquired Chaos Emeralds will become Super Emeralds and the player is given the opportunity to acquire the first Super Emerald. However, the player will not be allowed to return to Hidden Palace Zone via warp rings until they collect the remaining Chaos Emeralds. If by chance the player has not collected a single Chaos Emerald by Mushroom Hill and goes to Hidden Palace via the first warp ring, the player must exit the area by jumping on the teleporter in the bottom central part of the room. Once all 7 Super Emeralds are obtained, both Sonic and Knuckles have access to their even more powerful Hyper forms (Hyper Sonic and Hyper Knuckles respectively) once they have obtained all of the Super Emeralds.

Tails cannot normally gain Emerald powers but does so when he collects all Super Emeralds, taking on the form of Super Tails. He has no Hyper form but simply remains Super, with four Super Flickies flying around him that attack nearby enemies. Taking care to avoid all the Special Stages, it is possible to finish the game with only the 7 Chaos Emeralds, retaining their Super powers until the very end of the game. In this case the game endings will resemble the good endings from Sonic & Knuckles. This allows for a total of nine different endings — each character (Sonic and Tails together have the same as Sonic alone) has one with 0–6 Chaos Emeralds, one with all 7 Chaos Emeralds and 0-6 Super Emeralds, and the third with all 14 Chaos and Super Emeralds.

Cheats

 * Sound Test/Act Select: In Angel Island Zone, grab hold on a swinging rope and press the following in order: Left, Left, Left, Right, Right, Right, Up, Up, Up. (A Ring chime will sound if successful.) Then pause the game and press to return to the title screen. The Sound Test option should be available to select below "Competition".
 * Debug Mode: After accessing the Sound Test, play through either act of Mushroom Hill Zone and grab a hold on one of the manual elevators and press the following in order: Left, Left, Left, Right, Right, Right, Up, Up, Up. (A Ring chime will sound if successful.) Then pause the game and press to return to the title screen. Go to the Sound Test again then while highlighting any Act hold  before selecting the Act to start the Act with Debug Mode.

Re-releases

 * Sonic & Knuckles Collection (1997)
 * Sonic Jam (1997)
 * Sonic & Garfield Pack (1999)
 * Sonic Action Pack for PC (2000)
 * Sonic Action 4 Pack for PC (2001)
 * Twin Pack: Sonic CD and Sonic & Knuckles Collection (2002)
 * Sonic Mega Collection (2002)
 * Sega PC Mega Pack (2003)
 * Sonic Mega Collection Plus (2004)
 * Sonic Mega Collection Plus & Super Monkey Ball Deluxe (2005)
 * Sega Fun Pack: Sonic Mega Collection Plus & Shadow the Hedgehog (2009)
 * Sonic PC Collection (2009)
 * Sonic Classic Collection (2010)
 * Virtual Console (2010)
 * ''Sega Mega Drive Classic Collection Volume 3 (2010)
 * ''Sega Mega Drive Classic Collection Gold Edition (2011)
 * Sonic 3 & Knuckles for Steam (2011)

Triva

 * If using 'Debug mode' and a certain number of Super Monitors are destroyed at once, (most effectively with Insta-Shield) then the controls of the character will be locked and by pressing Start the game will turn back into Sonic & Knuckles.