Sonic - Hyper X is a 2004 hack of Sonic the Hedgehog created by Skaarg. It was one of the first Sonic hacks that had all of its music changed. In addition, it also featured modified palettes and layouts. Skaarg had stated that he was going to continue to expand upon his hack, but it seems highly unlikely at this point.

A great hack for Sonic the Hedgehog hack made by MarkeyJester features new enemies, layout, music,etc..Credits:3rd Act Layout - Gallium Grant.Gameplay Testers - iojnekns, snkenjoi, EditChrisBug finders - DAGarden, qiuu, Selbi, SonicVaan

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 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 and the Secret Extended Edition (previously known as Sonic 1: The Other Extended Edition, not to be confused with Sonic the Hedgehog Extended Edition) is a hack of Sonic the Hedgehog for the Sega Mega Drive/Genesis by Hayate. It was discontinued in August 2008, after Hayate gave up on the hack due to the various bugs it had, but it was picked up again in December 2009.

Sonic Next Genesis a hack of Sonic the Hedgehog inspired by a the 2006 game Sonic the Hedgehog but mostly contains custom content.Credits:RedHotSonic - Sonic 3K's Priority Manager in Sonic 2MarkeyJester - 128 Variation of Disassembly, Background Deformation Code, ASM GuideHiveBrain - Sonic 1 DisassemblyMercury - ReadySonicvladikcomper - Background Deformation EngineStealth - SonED2MainMemory - SonLVL and related programsXenowhirl - SonMapED, Sonic 2 Disassemblysnkenjoi - FlexTornado - Water Guide, Sonic 3 Sound Driver in Sonic 1 TutorialDemonFox - Caterkiller Fix for 3K's PriorityMoDule - Sonic 3K's Priority Manager in Sonic 2shobiz - Sonic 3K's Ring Manager in Sonic 2Sonic master and hitaxas - Splash Screen TutorialsKram1024 - Sonic 3K's Sound Driver in Sonic 1ValleyBell - SMPS Researchflamewing - SMPS2ASMDolphman - Genesis-style Sonic Advance badnik artx\\\_justicehunter\\\_x - Silver spritesDamien - Shadow SpritesThe creators of all the Sonic 1 and 2 Sonic Retro SCHG and SSRG tutorialsSSRG and everyone on itPeople who contributed art to The Spriters ResourceMy cat Nicole for sitting with me while I worked on thisAnd many other people I likely forgot to credit

Sonic 1 Pixel Perfect is a ROM hack of Sonic the Hedgehog for the Sega Mega Drive / Genesis by JcFerggy and NovaWizard. The hack features new extended layouts and art, custom loops and tubes, dynamic palettes for the acts, and a complete new Green Hill Zone layout (with edited boss) as of the first beta release.