Cursed Reflection

Corrupted Reflection. When a creature that can see the mirror monster's reflective face starts its turn within 30 feet of it, the monster can force it to make a DC 15 Wisdom saving throw if the mirror monster isn't incapacitated itself and can 'see' the creature. If the saving throw fails by 5 or more, the creature becomes instantaneously petrified. Otherwise, a creature that fails the save is rooted to the spot, staring at the monster's face and is restrained by their own body slowly turning to reflective glass. The restrained creature must repeat the saving throw at the end of its next turn, becoming petrified on a failure or ending the effect on a success. The petrification and glassification combination lasts until the creature is freed by the greater restoration spell or other healing-type magic.

Unless surprised, a creature is able to avert its eyes to avoid the saving throw at the start of its turn. If the creature does so, it can't see the mirror monster until the start of its next turn, when it can avert its eyes again. If the creature looks at the monstrosity in the meantime, it must immediately make the Wisdom saving throw.

If the cursed reflection sees itself reflected on a polished or otherwise reflective surface within 30 feet of it and in an area of bright light, the monster is, due to its own neverending curse, affected by its own corrupted reflection.

Multiattack. The monster makes either three melee attacks--one with its glass claws and two with its mace--or two ranged attacks with its hand crossbow.

Glass Claws. Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 16 (4d6 + 2) slashing damage

Mace. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) bludgeoning damage.

Hand Crossbow. Ranged Weapon Attack: +5 to hit, range 30/120 ft., one target. Hit: 5 (1d6 + 2) piercing damage plus 7 (2d6) poison damage.