Sonic the Werehog is a werewolf form of Sonic the Hedgehog. He gains less speed, but he has more strength. Sonic is able to become a werehog, due to Dr. Eggman tricking him into going into a machine, that would "free" him from the Dark Gaia. He used Sonic as a vessel, for the Dark Gaia to have some power, until he rises from the center of the earth. Sonic isn't able to control his werehog form; he transforms to a werehog at nighttime. In this form, he can extend his arms at far ranges, and can run on his arms and legs. Sonic's running shoes turns into spiky cleats when he transforms. His fingers also grow into claws, and his teeth grows into fangs. His ears are also more pointy and curve inward a little. His entire body is covered with fur. He can do powerful combat moves as a werehog.
Sonic turns into a werehog in Super Mario Silver Spurs: Episode Three. He takes this form to take on evil mutants, with the help of a possessed Gumball and Dry Bowser. Oddly enough, Sonic is able to control his werehog form in the movie, but only at night.