Locket of the Missing Twin

Hinged silver, with two oval frames inside, one holding a portrait and the other holding nothing but its own polished back.

Each charge raises a silent double of the wearer that copies them exactly for one minute. While the double stands, the first attack that would hit the wearer strikes it instead and destroys it; this costs no action and grants none. When depleted the empty frame still shows whatever stands behind the wearer.