Sonic 2 but keep Tails or else is a hack by GT Koopa where you should keep Tails from respawning or else you will recieve a Game Over

Sonic 2 Delta is a groundbreaking series of ROM hacks by famed Sonic scene member Esrael Neto, which restores several deleted levels and prototype elements to Sonic the Hedgehog 2 for the Sega Mega Drive / Genesis. Various features of Sonic 2 Delta, common across the series despite the existence of several versions/branches of the hack, include the use of art and music from the betas and Sonic the Hedgehog and re-implementation of badniks that had been removed from the final game. The level order of Sonic 2 Delta is also similar to the original intended order, rather than that used in the final version. The main version of this hack is entitled Sonic 2 Delta and was based upon the Simon Wai prototype, before version 0.24 transferred the codebase to 'revision 2' of Sonic 2 from Sonic Compilation. More information on the various lineages and their history is detailed in the section "Other versions" below. A hack similar in concept, called Sonic 2 Long Version, has been released by another hacker, Sonic Hachelle-Bee.

Sonic 2 Delta is a groundbreaking series of ROM hacks by famed Sonic scene member Esrael Neto, which restores several deleted levels and prototype elements to Sonic the Hedgehog 2 for the Sega Mega Drive / Genesis. Various features of Sonic 2 Delta, common across the series despite the existence of several versions/branches of the hack, include the use of art and music from the betas and Sonic the Hedgehog and re-implementation of badniks that had been removed from the final game. The level order of Sonic 2 Delta is also similar to the original intended order, rather than that used in the final version. The main version of this hack is entitled Sonic 2 Delta and was based upon the Simon Wai prototype, before version 0.24 transferred the codebase to 'revision 2' of Sonic 2 from Sonic Compilation. More information on the various lineages and their history is detailed in the section "Other versions" below. A hack similar in concept, called Sonic 2 Long Version, has been released by another hacker, Sonic Hachelle-Bee.

Sonic 2 Dimps Edition is a hack of Sonic the Hedgehog 2 by Spanner. This hack attempts to mimic what Sonic 2 may have been like if it were created by Dimps. This means incorporating many features found in Dimps games such as random speed boosters. This does not include features common in most modern Sonic titles with the exception of a homing attack. The hack was discontinued due to various reasons and there was currently no intention to return to it, except that somebody else now has the source code and is intending to finish off the job. Version 1.5 was uploaded to fix some reported bugs.

Sonic 2 EX (often abbreviated as S.EX) is a hack of Sonic the Hedgehog 2 for the Sega Mega Drive/Genesis by Mr. EX. Its highlights include spring-based layouts like those of Project Shadow 2, new art and layouts, and original music.

Sonic 2 Megamix is the first installment in the Megamix series of hacks by Team Megamix, followed by Sonic Megamix. It was created by Tweaker for submission in the 4th Hacking Contest. It features edited palettes and music.Future plans were to revamp the hack, including moving it to a split disassembly and revamping the level layouts; the former of which has already been completed. It was also to contain various pieces of original music, as well as imports from other games, such as Sonic Advance 2, or Sonic Jam.

Sonic 2 Millennium Edition is a palette and layout hack of Sonic the Hedgehog 2 for the Sega Mega Drive/Genesis by Striker.

Sonic 2 Recreation is a hack of Sonic the Hedgehog 2 (16-bit) by redhotsonic. It sports an ASM overhaul, multiple characters, new zones, a new boss, a new DAC driver that supports many different sound features, new zone art.

Sonic 2 Retro Remix is a large-scale ROM hack of Sonic the Hedgehog 2 for the Sega Genesis / Mega Drive, created by Thorn and DNXDelta. The goal of the project is to create a 2D Sonic the Hedgehog game that requires exploration to progress, as well as the requisite platforming and sheer speed. A mission system akin to those of the 3D Super Mario games is implemented as the means of progressing from one level to the next. Missions involve earning Chaos Emeralds in scavenger hunts, boss battles, speed runs and score attacks; most require learning each level's ins and outs, instead of just finding the easiest way to the goal.

Sonic 2 Revamped was a heavy modification of Sonic the Hedgehog 2 created by Irixion. This mod first started out as a layout hack, a test of skill, and what Irixion could do. At the time, it didn't have a name, but after seeking for someone who could help, Tweaker suggested the name Sonic 2: Revamped, and it stuck ever since. It eventually grew into a few close friends helping out, and the project grew into realizing Irixion's vision of the perfect game. After major setbacks and a core crippling incident, the hack was ultimately scrapped.