Kirby in Sonic the Hedgehog 2 is a hack of Sonic the Hedgehog 2 by Lone Devil (Also known as Darkon360) for the Sega Genesis/Megadrive. It features Kirby and Waddle Dee whom replaces Sonic and Tails as the lead protagonists. Kirby can inhale monitors and most enemies but cannot copy their abilities. Lives function as health points and the only way to obtain them is grabbing every 50+ Rings, Checkpoints/Lampposts, Randomized 1Up Monitors, or Score every 50000+ points. The hack also features 4 difficulty modes. Hidden Palace is restored but only as a 1 Act Zone for Kirby, located somewhere in Mystic Cave Act 2.

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).

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.

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.

Motobug the Badnik in Sonic the Hedgehog (aka Motobug in Sonic 1) is a hack of Sonic the Hedgehog for the Sega Mega Drive, by Polygon Jim. As its title suggests, in this hack the main character Sonic the Hedgehog is replaced by Motobug, one of Dr. Robotnik's badniks.So far, some of Sonic's main sprites and animations have been replaced by those of Motobug, Motobug's speed has been decreased (except when powered-up by aSpeed Shoes monitor, which are more numerous), and the sprites of Roller badniks in Spring Yard Zone have been replaced by those of Sonic (referencing a common interpretation by fans that Roller is a robotic impersonation of Sonic, something that officially appeared in later games in the form of Metal Sonic and various others).Of the first release, Polygon Jim stated that he had only tested and confirmed Green Hill Zone (Acts 1-3) for completability. However, upon testing, Katelynn andRGamer2009 reported that other Acts are completable, including:Marble Zone Act 1Spring Yard Zone Acts 1 and 2Labyrinth Zone Acts 1 and 2Star Light Zone Acts 2 and 3Final Zone

A hack based on Sonic the hedgehog 2 made by snkenjoi Aperture Science's Portal Gun finds its way into Sonic 2.The portals in the game actually affect objects other than sonic - to the extent that you can kill an enemy with its own projectile if you fling it back at it.Credits:E-122-Psi - sonic's spritesheetflamewing - help with collision detectioniojnekns - portal spritesFraGag - testing

Ray the Flying Squirrel in Sonic the Hedgehog is a fan-made ROM of the game Sonic the Hedgehog for the Sega Mega Drive/Genesis, featuring the character Ray the Flying Squirrel in place of Sonic the Hedgehog, the game's usual protagonist. The creator of the hack is Fabricechaotix.Ray the Flying Squirrel has a air glide move similar to Knuckles but the air glide does no damage when touching enemies. The air glide also does not stop when touching walls. Unlike many Sonic 1 hacks there is no spin dash move.