Sonic ZX (v1.0) (S1 Hack) is a ROM hack of the original Sonic the Hedgehog game for the Sega Genesis. The ‘ZX’ designation might refer to a specific internal version name or a theme. It being an S1 Hack implies that it modifies the first Sonic game. The version number (v1.0) suggests an initial release.  More information would be needed to understand the specifics of its modifications and gameplay. Its nature as a hack reflects the ongoing engagement of the community with the original game.

Sonic ZX (v1.0) (S1 Hack)

Sonic Xero v3.0 final (fixed)