Haunted Zone monsters

The Haunted Zone monsters are evil creatures that rise from the Underworld and roam the Haunted Zone once per year on Halloween Night. Their bodies are covered in shaggy green fur and they have pig snouts, sharp fangs and long, pointed tails. Each monster wears a Charm of Despair around their necks, which allows them to return to the Underworld at midnight.

Mobians who spend Halloween Night in the Haunted Zone may be corrupted by the evil of the Zone. The monsters give these individuals their own Charm of Despair, and if they are still wearing it at midnight they will return to the Underworld with the monsters; it is implied that they become monsters themselves.

History
One Halloween, Sonic and Tails went to spend the night in the Haunted Zone. Sonic was quickly taken over by the evil of the Zone and tried to attack Tails. The monsters gave Sonic a Charm of Despair. Fortunately, Tails managed to steal Sonic's Charm before midnight, preventing him from returning to the Underworld with the monsters and breaking the spell. Sonic had no memory of the night's events and assumed he had fallen asleep, although Tails still had Sonic's Charm of Despair.