Skeleton Keys

History
Regina's skeleton keys are an item from Fairytale Land, and they have a skull on them. They appear to grant her access to the entire town of Storybrooke, or at least to select locations, although precisely how remains a mystery.

Early on, her skeleton keys open the crypt where she keeps a collection of locked boxes that mimics her collection from Fairytale Land. She uses these keys to withdraw the Huntsman's heart. Later, as Mr. Gold recommends during their deal negotiation, she hides a skeleton key in Mary Margaret's cell to encourage her to escape from jail. Mary Margaret finds this key and uses it to escape. Both Mary Margaret and Emma believe that Regina must have planted the key since, after all, it was one of her skeleton keys.

When August installs the lock on Mary Margaret's door in The Return, she comments that she is relieved as long as the lock keeps Regina from using her "skeleton keys" to get into their apartment. Mary Margaret and Emma also believe that Regina used these keys to break and plant the evidence that would frame Mary Margaret.