Knuckles the Echidna in Sonic the Hedgehog2006

Metal Sonic in Sonic the Hedgehog 2 swaps Sonic out for Metal Sonic from Sonic CD, you can choose between the Original moveset, Sonic CD, or the 2011 remaster moveset from Christian Whitehead's port of Sonic CD Metal will once show Robotnik he's not a bot to be forgotten...

Amy in Sonic 1 is a modification of Sonic 1 that swaps sonic out with Amy Rose from Sonic CD, bringing with her, her move-set from Sonic Advance. Using Her Piko Piko Hammer she will have to Jump, whirl, and dash through South Island to put a Stop to Robotnik's plans.

Amy Rose in Sonic the Hedgehog 2 swaps Sonic out for Amy Rose from Sonic CD, equipped with her Sonic Advance moveset. She will have to Jump whirl and Dash through Westside Island with the help of her newfound friend Tails! Infiltrate the Death Egg and put a stop to the deadly Space Station using your hammer!

Charmy Bee in Sonic 1 is a modification of Sonic the Hedgehog where Sonic is swapped out with Charmy Bee from Knuckles' Chaotix. Charmy bee cannot jump instead he can only fly, so he must use this ability to put a stop to Dr.Robotnik's plans and robot army, storm the Scrap Brain and collect the chaos emeralds!

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.

This is a hack which changes Sonic the Hedgehog for Genesis into a entirely different game with new gameplay. It stars Dr. Robotnik whom must capture creatures with a net and put them in creature capsules. The graphics are the same as previous Sonic games but the rest is mostly changed. Most levels are open by default.

Sonic 2 XL is a hack of Sonic the Hedgehog 2 for the Sega Mega Drive by Captain Bozo and Ranger. Rings are replaced with onion rings, and Sonic becomes fatter after eating them.