Gex the Gecko in Sonic the Hedgehog2020

This ROM hack swaps Sonic and Tails for Mighty and Ray, with adapted abilities inspired by their Sonic Mania versions.

Sonic 2: Pink Edition is a modification of Sonic 2 that replaces Sonic & Tails with Amy and Cream as playable characters, Amy's sprite being based off her modern design. The changes aren't just to the asthetics though, Amy and cream bring their own movesets to the table! Amy bringing her trusty Piko Piko Hammer to swing,jump,whirl and dash through Robotnik's obstacles. Cream bringing the spindash and ability to fly, oh! don't forget about her trusty Chao, Cheese who can attack enemies, even bosses, from a distance!

Bunnie Rabbot in Sonic the Hedgehog 2 allows players to replace Sonic with Bunnie Rabbot as the playable character in the original Sonic the Hedgehog 2 game.

A ROM hack that swaps Sonic for Cream and Cheese (from Sonic Advance). Cream can fly like Tails, spindash and use Cheese to attack enemies remotely.

The citizens of Mobius just can't seem to catch a break. Dr. Robotnik (AKA Eggman) is yet again up to his no good tricks. Factories and pollution are spreading like wildfire as he's once again trying to take over the world. Fortunately, the Sonic Heroes are never at rest, and once again wage their battle to defeat Eggman's evil forces. However, the heroes have landed in double jeopardy. Eggman's madman descendant, Eggman Nega, has escaped from the Ifrit's dimension, and is wreaking his usual havoc in an effort to destroy the world. He's even captured Eggman's top three lieutenants, the ruthless Team Metallix, and reprogrammed them to do his even more evil bidding. Unlike previous instances of Nega's destruction, Eggman is not fazed. He figures that once he's in control of the world, he can take care of Eggman Nega as he pleases. Unfortunately for Eggman, Sonic the Hedgehog isn't having that. Before he can decide who to dispatch where, he receives a call through the communicator Tails gave him. The message: someone's already on the case. Not just someone, but someones! Apparently, Sonic's very own sister, Sonia the Hedgehog has already caught wind of Nega's evil and is out to stop him. Sonic is a bit eased, knowing full well of his sister's strength and agility. She also lets him know that she has found and teamed up with a mysterious young hedgehog who can move things with his mind. Sonic instantly recognizes that Sonia is with his newest ally: Silver the Hedgehog. Silver has once again traveled through time to ensure that the future is free of Nega's tampering (though he really ought to just stay here in the present, you know). Knowing that the two hedgehogs are more than capable of handling the situation, Sonic leaves it to them, and resumes dealing with Eggman. Eggman Nega is well aware that Sonic is busy with his dimwitted ancestor. However, he'd do best not to overlook a certain factor. The S Factor, Sonia and Silver! It's up to you to lead the unlikely tag team of the physically powerful Sonia, and the psychokinetic Silver on their quest to right the wrongs of the evil Eggman Nega!

Mega Man X in Sonic The Hedgehog 2 is a ROMhack/mod of Sonic The Hedgehog 2 which lets the player control Mega Man X instead of Sonic, with all of his signature attacks, like the charge beam, the wall jump and the dash, and X can also get the weapons from his enemies, like in his own games.

Knuckles' Emerald Hunt is a modification of Sonic the Hedgehog 2 that split off from another hack Sonic 2 Adventure Edition. It's main goal is to mimic the Emerald Hunting Gameplay from Sonic Adventure 2/Battle. Playable characters being Knuckles and Tikal, through each stage you must find and collect 3 Emeralds or Emerald pieces. The Game features the radar from SA2, and a secret Sandwich mode in which all the emeralds are replaced with Sub sandwiches and the Master emerald is replaced with a Subway footlong. It also features the Scrapped Hidden Palace Zone and some Sonic 1 Zones

Sonic the Hedgehog Megamix (commonly shortened to Sonic Megamix) is a work-in-progress multiperson disassembly modification of the original Sonic the Hedgehog videogame for the Sega Mega Drive / Genesis, developed by Team Megamix and more recently moved to the Sega Mega-CD. The game features the ability to play as one of five different characters: Sonic the Hedgehog, Mighty the Armadillo, Shadow the Hedgehog, Miles "Tails" Prower, and Knuckles the Echidna. It is an extensive reworking of the original game, featuring new art, music, abilities, layouts, and other things.