Rouge the Bat in Sonic 1 is a fan-made ROM hack of the original Sonic the Hedgehog for the Sega Genesis. It features the character Rouge the Bat, from the Sonic Adventure games, integrated into the original Sonic game's levels and gameplay. This modification changes elements of the original game, adding new challenges and character dynamics.  It's not an officially released title by Sega. The development is done by the fans and the ROM hack is distributed online.

Rouge the Bat in Sonic 1

Rolo to the Rescue (USA, Europe)