Vector the Crocodile in Sonic the Hedgehog (aka Vector in Sonic 1) is a hack of Sonic 1 by E-122-Psi, starring Vector the Crocodile as the playable character instead of the blue hedgehog. The game is modified to use Vector's sprites (edited from Knuckles Chaotix) in place of Sonic's, along with several modifications to the player's stats and abilities.
The game was modified by Sonic Retro member E-122-Psi, with additional programming and coding by other members including MarkeyJester and flamewing.
