A longplay for Sonic 1 hack is Shadow the Hedgehog in Sonic the Hedgehog.
Shadow the Hedgehog in Sonic the Hedgehog (aka Shadow in Sonic 1) is a fan-made ROM of the game Sonic the Hedgehog for the Sega Mega Drive/Genesis, with Shadow the Hedgehog as a playable character in place of Sonic the Hedgehog.
The game was modified by Sonic Retro member FeliciaVal, with additional programming and coding by other members including Jimmy Hedgehog, Selbi, MarkeyJester and E-122-Psi. Most of the sprites were taken from a sprite sheet at this page (direct link does not work, copy and paste instead).
Mostly due to Shadows palette being shared with other sprites, several colors are changed. This means grey springs, grey Crabmeats, and many other changes.