Mirror Life. The Mirror Dead is trapped in a mirror and cannot leave it unless the mirror is destroyed or it uses its Mirror Teleport reaction. Whenever the Mirror Dead's mirror is destroyed she teleports to the nearest reflective surface. While within the mirror the Mirror Dead can use an action to become invisible while outside of combat and cannot be attacked or dealt damage.

Horrifying Visage. Each non-undead creature within 60 feet of the Mirror Dead that can see her must succeed on a DC 13 Wisdom saving throw or be frightened for 1 minute. A frightened target can repeat the saving throw at the end of each of its turns, with disadvantage if the Mirror Dead is within line of sight, ending the effect on itself on a success. If a target’s saving throw is successful or the effect ends for it, the target is immune to the Mirror Dead’s Horrifying Visage for the next 24 hours.

Slaying Visage. The Mirror Dead twists her appearance so that those who see her begin to bleed from the eyes. This affect has no effect on constructs and undead. All frightened creatures within 30 feet of her that can see her must make a DC 14 Constitution saving throw. On a failure, a creature drops to 0 hit points. On a success, a creature takes 28 (8d6) necrotic damage and is blinded until it receives magical healing or finishes a long rest.

Mirror Teleport. As a reaction to a creature not being able to see the Mirror Dead it can teleport to a reflective surface visible to the triggering creature.