Any creature other than you that sees its reflection in the activated mirror while within 30 feet of it must succeed on a DC 15 Charisma saving throw or be trapped, along with anything it is wearing or carrying, in one of the mirror's twelve extradimensional cells. This saving throw is made with advantage if the creature knows the mirror's nature, and constructs succeed on the saving throw automatically.

An extradimensional cell is an infinite expanse filled with thick fog that reduces visibility to 10 feet. Creatures trapped in the mirror's cells don't age, and they don't need to eat, drink, or sleep. A creature trapped within a cell can escape using magic that permits planar travel. Otherwise, the creature is confined to the cell until freed.

If the mirror traps a creature but its twelve extradimensional cells are already occupied, the mirror frees one trapped creature at random to accommodate the new prisoner. A freed creature appears in an unoccupied space within sight of the mirror but facing away from it. If the mirror is shattered, all creatures it contains are freed and appear in unoccupied spaces near it.