Knuckles in Sonic the Hedgehog is a fan-made ROM of the game Sonic the Hedgehog for the Sega Mega Drive/Genesis, featuring the character Knuckles the Echidna in place of Sonic the Hedgehog, the game's usual protagonist. The history of the game begins with the release of the Mega Drive game Sonic & Knuckles. The unique cartridge featured "Lock-On Technology" and allowed players that also owned the game Sonic the Hedgehog 2 to link the two together and play the game through as Knuckles instead of Sonic. However, partly because of a poorly matching colour palette, no such feature was included in the first Sonic game (instead, attaching Sonic 1 to the Sonic & Knuckles cartridge unlocked the full version of Blue Sphere). In the ROM hacking community, creating a patch that allowed the gamer to play as Knuckles in Sonic the Hedgehog was considered the "Holy Grail of ROM Hacking." On September 1, 2005, Stealth created a hack that allowed a player to do just that. His hack was called Knuckles the Echidna in Sonic the Hedgehog (Knuckles in Sonic 1, or S1K for short) Knuckles in Sonic 1 one gives Knuckles all the moves he has in Sonic and Knuckles, including gliding, wall climbing, and the spin dash. Not only that, Knuckles can transform into his Super form once he obtains all the emeralds (a cheat must first be enabled).

A reverse (and sequel) of an earlier Sonic 2 hack I did called "Keep Tails Or Else." You have 30 seconds to get rid of Tails otherwise you get a game over. Clearing the challenge immediately warps you to the next act. Go for the highest score!The hack made by T Koopa

Mecha Sonic in Sonic the Hedgehog (aka Mecha Sonic in Sonic 1) is a hack created as a proof-of-concept by Iron Sonic of Sonic the Hedgehog for the Mega Drivein which the player plays as Mecha Sonic from Sonic & Knuckles. The controls are the same as in the original Sonic 1, save for the ability to perform the Spin Dash. Each sprite has been edited, and the player size and other aspects of the Sonic object have been changed to accommodate Mecha Sonic's larger size.Whilst the game is mostly playable, there are certain areas in the game that Mecha Sonic cannot complete due to his increased size; prime examples of this includeSpring Yard Zone and Scrap Brain Zone.

Metal Sonic in Sonic 3 & Knuckles is a hack of Sonic the Hedgehog 3 & Knuckles. It was created by Darkon360/GothicReaper/LoneDevil. Metal Sonic is playable, complete with additional special moves.

Metal Sonic in Sonic the Hedgehog is a hack of Sonic the Hedgehog created by Darkon360/GothicReaper/LoneDevil. It stars Metal Sonic as the playable character instead of Sonic the Hedgehog. The game is modified to use Metal Sonic's sprites in place of Sonic's. The hack comes with 4 different play styles: The Original, Sonic 2Spindash, Sonic CD, and Sonic CD 2011.

Metal Sonic Rebooted is a complete heavy modification of Sonic the Hedgehog 2 by Lone Devil for the Sega Genesis. it features an extensive amount of new art, layouts, mechanics, music, and features that in total creates a different experience.StoryDr'Robotnik has built an advanced army of badniks to search for the Chaos Emeralds, and it's up to Metal Sonic to find the emeralds before them by destroying everything in his way to show Robotnik he shouldn't be replaced.CreditsKCEXE - Music and SFX ports from various Genesis/Megadrive gamesEduardo Knuckles - Music for Magma FactoryClownacy - Sonic 2 Clone Driver v2Dark Sonic - Hardware Testing for v1.1

Mighty the Armadillo in Sonic the Hedgehog (aka Mighty in Sonic 1) is a hack of Sonic 1 by E-122-Psi, starring Mighty as the playable character instead of Sonic the Hedgehog. The game is modified to use Mighty's sprites in place of Sonic's, along with several modifications to the player's stats and abilities.