Sonic the Hedgehog Genesis (Genesis) is a hack of Sonic the Hedgehog by Xenowhirl which attempts to recreate certain aspects of the Game Boy Advance Sonic 1 port titled Sonic the Hedgehog Genesis.
- Physics which closely match those of the GBA game, noticeable during Eggman confrontations.
- Spin Dash which has slow animation and dust that appears slightly before the spin starts.
- Background effects, like moving clouds.
- Fixed Caterkiller-damage bug, scrolling-left-too-fast bug, die-during-level-resize bugs.
- Applied a Left boundary teleport fix, signpost art loading and collision fix, skippable score countdown, "walking jump" fix, momentum preservation, "press start" fix and edits, altered rebound physics, altered jump physics, etc.
- Sonic's sprite art and the life counter text are replaced with the different art from S1GBA.
- The scrolling is changed to give a better sense of speed and Sonic CD-style lookahead (that's not in S1GBA, but neither is a bigger screen).
- All springs double Sonic's max speed until landing if airborne before the spring counter runs out. All side-facing red springs act like yellow springs. To compensate for the lower speed, slope repel calculations aren't performed after hitting a spring. Vertical springs erase all horizontal velocity not in a direction being pressed.
- Slowdown and pop-in are not present.
- Landing on steeply curved ground, still acts much like the original Sonic 1 and sometimes conflicts with the momentum preservation.
- Sonic 1 GBA has Sonic starting off GHZ1 at a location further to the left.
- Rising platforms in GHZ are not solid.
- The dynamic level resizing is not changed.
- The switch under the monitor in Labyrinth Zone needs to be removed.
- The momemtum preservation against upside-down spikes is not changed.
- The first Buzz Bomber does not fly high enough.
- Music should continue playing and not restart after losing a life.
- Music is not remixed.
- No Game Save function.
Release thread on Sonic Retro