Mortal Kombat II Unlimited is a full scale hack of the Sega Genesis Mortal Kombat II game, Originally work on the hack ceased with version 07, but in 2011 version 1.0 was released which added many new graphical features. Added a combo system;Secret fighters now fully playable;Bosses now fully playable;More new sounds;New Select Screen and Main Menu;New stages and music from Mortal Kombat 1;New moves such as Brutality;New Game Modes such as Practice and Endurance;Returned biographies/Endings/Intro/VS-screens from the arcade version;and many more…

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 Robotnik's badniks.So far, some of Sonic's main sprites and animations have been replaced by those of Motobug, Motobug's speed has been decreased (except when powered-up by aSpeed Shoes monitor, which are more numerous), and the sprites of Roller badniks in Spring Yard Zone have been replaced by those of Sonic (referencing a common interpretation by fans that Roller is a robotic impersonation of Sonic, something that officially appeared in later games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

Mr. Needlemouse is a hack of the original Sonic the Hedgehog game for the Sega Mega Drive / Genesis, by MKAmeX. It replaces Sonic the Hedgehog with one version (arguably the strangest) of his designer Naoto Ohshima's early prototype of the character, Mr. Needlemouse. Planned features include a complete overhaul of the game's graphics to resemble early concept art, and perhaps new music.

Mutant League Hockey is a hockey game that was released in 1994 for the Sega Genesis. This video game is a spin-off of Mutant League Football and features several of the same team names and players as well as new ones.

Mystic Defender is a two-dimensional action video game released for the Sega Genesis system. Originally titled Kujakuō 2: Geneijō (孔雀王2?) in Japan and based on the anime/manga Kujaku Ou, it is the sequel to SpellCaster for the Sega Master System.