Charm of Despair

A Charm of Despair is an evil, magical amulet worn around the neck that allows the wearer to return to the Underworld. Each of the Haunted Zone monsters wears such an amulet, and they give Charms of Despair to any Mobians spending the night in the Haunted Zone who are corrupted by the Zone's evil. It is implied that individuals wearing a Charm of Despair who return to the Underworld at midnight become one of the Haunted Zone monsters.

Sonic the Hedgehog received a Charm of Despair when he was possessed by the evil of the Haunted Zone when he stayed there on Halloween. Moments before midnight, Tails managed to steal the Charm, preventing Sonic from returning to the Underworld with the other monsters and breaking the spell. Sonic had no memory of the night's events and assumed he had fallen asleep, although Tails still had the Charm of Despair as proof.

Trivia

 * An editorial footnote in the story explained that an amulet is something that is worn to keep away evil, the opposite of the Charm of Despair's purpose in the story.