Firefly is an enemy Badnik encountered in Volcano Valley Zone, the fifth level of Sonic 3D: Flickies' Island.
Resembling a fire-red mosquito, this Badnik will buzz around a set point in an erratic manner. It has no active defensive or offensive techniques; the only way this bot can hurt Sonic is if the hedgehog bumps right into it. Attack with a Spin Dash or jump. Smash it to recover its organic battery power source, a blue Flicky, and make Flickies' Island a slightly less dangerous place.
The name of this Badnik is conjectural, as no official name has been given to it. The name comes from the level editor in a development build of Sonic 3D that is included as a bonus feature in Sonic 3D: Director's Cut. Jon Burton has confirmed that the name was used in the original game.