Hexmirror

A hexmirror can absorb any curse, no matter how benign or malevolent the individual. Similarly, it can also bestow that same curse onto any creature, regardless of its nature or intentions with only a glance into the mirror. These types of mirrors are often encountered in the possession of individuals that practice dark magic, cast curses or have been cursed themselves. They are also sought after by those desperate to rid themselves of curses, despite the moral quandaries of possibly passing their affliction onto another individual. They are sometimes covered with a heavy black velvet cloth to prevent a person from accidentaly gazing into the mirror and becoming cursed. They come in a variety of sizes, some are the size of a handmirror, whilst others can fill the wall of an entire room. It is believed that stronger curses require bigger mirrors to hold them.

Activation

Trigger. The magic of the mirror is activated as soon as an individual sees its own reflection in it, even if briefly.
  Effects. When it is triggered, one of two things will happen. Whenever a creature that is Cursed looks into this mirror, and the mirror holds no curse, they are no longer Cursed and the mirror itself absorbs the curse as soon as they look away from it. If the mirror has absorbed a curse, a creature that looks into the mirror instantly receives that curse, thus becoming Cursed as the mirror loses the curse it had previously absorbed. If a creature is already Cursed in another way, it can still become Cursed by the mirror. A creature cannot lose any curse by looking into the mirror as long as they are Cursed by the mirror.  

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Countermeasures

The easiest way to avoid the effects of a Hexmirror is to not look into it. Covering your eyes or the mirror is the easiest way to prevent any curse from being exchanged.   Countermeasure Phases

Phase	Ability Check
Detection	Perception (DC 8), Detect Magic (Necromancy)
Analysis	Arcana (DC 12)
Solution	Attack (AC 12, 5 hit points)

  Solution (Attack). Read the following text when a character makes an attack against the mirror that reduces its hit points to 0. Note that if they attack with their eyes closed, they make the attack with disadvantage.
     

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Alternative Solutions

Arcana. Obscuring or chaning vision through a spell such as Darkness, Fog Cloud, Invisibility or even Blindness/Deafness. An anti-magic field also fully prevents the mirror from exchanging curses.
  Wisdom. Covering the mirror with a cloth, tarp or other object but doing so with eyes closed.