Knuckles the Echidna in Sonic the Hedgehog 2, or simply Knuckles in Sonic 2, is a platform video game that is part of the Sonic the Hedgehog series. It is the result of locking-on Sonic & Knuckles with Sonic the Hedgehog 2 using the former cartridge's unique "lock-on" technology. This game is essentially identical to Sonic the Hedgehog 2, with the exception of Knuckles the Echidna starring as the main playable character.
Knuckles the Echidna in Sonic the Hedgehog 2 is a 2D side-scroller platform video game with the exact same gameplay as in Sonic the Hedgehog 2 and Sonic & Knuckles. The only playable character here is Knuckles, who retains his moveset from Sonic & Knuckles.
- The title screen shows Knuckles instead of Sonic and Tails. Here, he uses the sprites from the title screen of Sonic & Knuckles.
- The 2P Player VS and Options menu have been removed from the title screen. As such, there is only simply a "Press Start" option, resembling the title screen of the original Sonic the Hedgehog.
- The color palettes for the Act title cards are colored green, red and yellow instead of blue, red and yellow.
- The Shield is colored gray instead of its usual blue.
- The Signpost will spin to the portrait of Knuckles portrait instead of Sonic (or Tails). It appears to be reused from Sonic & Knuckles.
- Secrets such as 1-Up Monitors have been added in the Acts for Knuckles to discover.
- When Knuckles respawns at a Star Post after losing a life or finishing a Special Stage, he will retain the number of Rings he had when he touched it.
- The Ring requirements in Special Stages to pass each checkpoint are notably lower than before, making the Special Stages much easier for Knuckles.
- Special Stages do not display Knuckles' name like Sonic and Tails'.
- To transform into Super Knuckles, the player has to hit the jump button twice, as opposed to the original Sonic the Hedgehog 2, where the player could turn into Super Sonic by simply jumping.
- In addition, the player cannot transform into Super Knuckles after touching the Signpost or pressing the switch on the Capsule.
- In Debug Mode, the player is limited to placing a Ring or a Super Ring Monitor.
- Act Select: At the title screen, the player has to press the following buttons in order: Up, Up, Up, Down, Down, Down, Left, Right, Left and Right. A Ring chime will sound if successful. They, they have to hold and press "Start" to access the Act Select.
- Debug Mode: At the Act Select's Sound Test, the player has to play the following tunes in order: 01, 09, 09, 04, 01, 00, 01, 08. A Ring chime will sound if successful. Then, they can highlight any Act and select it while holding to start an Act with Debug Mode.
- All 7 Chaos Emeralds: At the Act Select's Sound Test, the player has to play the following tunes in order: 01, 06, 07, 07, 07, 02, 01, 06.
- Sonic Jam (1997)
- Sonic Mega Collection (2002)
- Sonic Mega Collection Plus (2004)
- Sonic Mega Collection Plus & Super Monkey Ball Deluxe (2005)
- Xbox Live Arcade (2009)[note 1]
- Sega Fun Pack: Sonic Mega Collection Plus & Shadow the Hedgehog (2009)
- Sonic PC Collection (2009)
- PlaySEGA (2009)
- Sonic Classic Collection (2010)
- Virtual Console (2010)[note 1]
- Sega Ages: Sonic the Hedgehog 2 (2020)
- Though Sonic and Tails are replaced by Knuckles and locked by default, Tails is still piloting the Tornado in Sky Chase Zone and during the ending of the game.
- In the 2013 version of Sonic the Hedgehog 2, Knuckles was added as a playable character, allowing the player to play as him the same way as in Knuckles the Echidna in Sonic the Hedgehog 2. However, the color palletes of the Act title cards and the Shield were reverted to back to their original colors when playing as Knuckles.
- Knuckles' arms are miscolored tan in Special Stages.
- The Debug Mode code (01, 09, 09, 04, 01, 00, 01, 08) references the release date of Sonic & Knuckles (18 October 1994).
- This is also the reference used to enable Debug Mode in Sonic the Hedgehog 2.