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) down the elevator in the Library. As they walk through the tunels, Regina notices that Hook has a brazalet that belonged to her mother, and she asks him to give it to her, not knowing it would later rip her magic abilities later.

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, and she pushed Hook to the risk, after she calls him the "destraction" she needs to get the trigger from what once was Snow White's glass coffin, also located there.

Tamara and Greg Mendell activate the brazalet 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, without knowing what it is. Some time later, after Greg finds his father's body burried in their old campsite, Tamara reveals she has learned the uses of the gem: it could be used to destroy Storybrooke for ever from this world, which is exactly what they want to do.