Sonic 2: Advanced Edit is a Sonic 2 hack created by rika_chou. Sonic 2: Advanced Edit has seen 4 major releases. The 4th release includes the levels from the 3rd release as bonus content.
After putting the finishing touches on his new time machine, the prestigious Dr. Tang steps back to admire his life's work only to see it vanish before his very eyes. Waking up hundreds of years in the past, the doctor's young and careless neighbor soon realizes the shocking mistake he made while playing around in the laboratory. Pursued by hordes of fierce demons, will he survive long enough to retrieve the time machine and return home?
Tails in Sonic 1 is a hack of Sonic the Hedgehog for the Sega Mega Drive/Genesis originally created by drx which featured Tails as a playable character instead of Sonic. Tails can fly, spindash and swim in the same way that he can in Sonic 3.
Robotnik's Revenge is a hack of Sonic the Hedgehog 2 by ColinC10. It is a "boss rush" hack, in which all seventeen bosses from Sonic the Hedgehog and Sonic the Hedgehog 2 are fought in a somewhat arbitrary order over the course of a single level. The game takes place in Death Egg Zone from Sonic 2, and is meant to imply that there is more to the ship than there is in the original game.
Time spent completing the boss run is kept and the total time is given at the end of the course, along with a ranking. In Time Attack mode there are infinite lives and rings that can be found in-between battles. In survival mode, there are only 3 lives and no rings.
This ROM hack adds the Spindash from later Sonic games (and ports) and fix the notorious "Spike Bug", which causes the player to die after falling in a spiked pit.
Romhack of Ultimate Mortal Kombat 3 for the Sega Genesis. It adds new characters, with a total roster of 50 playable characters. It also adds backgrounds, new moves, combos, finishing moves, and missing audio samples are restored.