Trigger

The Trigger is an item featured on ABC's Once Upon a Time. It first appears in the twentieth episode of the second season.

After the Curse
In Storybrooke, Regina (accompanied by Hook) travels down the elevator in the Library. As they walk through the tunnels, Regina notices that Hook is wearing a bracelet that belonged to her mother, and she asks him to give it to her. Hook reliquishes the bracelet to her and she places it on her wrist.

They arrive to the huge cave in which Maleficent is trapped, kept alive in any form she has by a spell that does not let her die. Regina explains she needed to protect that cave because it is where the trigger is hidden. She pushes Hook to the risk, calling him the "distraction" she needs to retrive the trigger from what once was Snow White's glass coffin.

Tamara and Greg Mendell activate the mechanism they placed within the bracelet, making Regina's magic useless. They kidnap her and Tamara steals the trigger from her. At the Storybrooke Cannery, Tamara shows the gem to Greg. Neither one knows what it is. Some time later, after Greg finds his father's body burried in their old campsite, Tamara reveals she has learned the use of the gem: it can be used to destroy Storybrooke from this world forever, which is exactly what they want to do.