The frame of this withered demon’s corpse barely fills the ash-colored plate armor that encases it. It carries a serrated khopesh sword in spiked gauntlets that hiss with violet smoke, and a horned ivory mask devoid of features is nailed to its face.

Children of Fiends. Long ago, a demon lord of shadow and deceit fell in love with a demon goddess of destruction. At the base of a crater left by a meteor that destroyed a civilization, the two devised a plan to not merely slay their peers, but wholly expunge them from time itself, leaving only each other. Shortly thereafter, the mask wights were conceived.

Rites of Annihilation. To create these undead, the lord of shadows stole the bodies of death knights from beneath the necropolis of an arch-lich. Then, the goddess of the underworld sacrificed a million condemned souls and drained their essence into ivory masks—one for each fiend the couple sought to annihilate. Finally, the masks were hammered onto the knights with cold iron nails, and their armored husks were left at the bottom of the memory-draining River Styx for 600 years.

When they rose, the mask wights marched out into the planes to bury knowledge, conjure secrets, and erase their quarry from memory and history.

Ready for Betrayal. Kept secret from one another, though, the two each created an additional mask wight, a safeguard for in case betrayal should cross their lover’s mind.

Undead Nature. A mask wight doesn’t require air, food, drink, or sleep.

Mask Wight

Medium undead, neutral evil
Armor Class 19 (natural armor)
Hit Points 207 (18d8 + 126)
Speed 40 ft.

STR	DEX	CON	INT	WIS	CHA
22 (+6)	18 (+4)	24 (+7)	15 (+2)	16 (+3)	18 (+4)

Saving Throws Str +11, Dex +9, Con +12, Int +7, Wis +8, Cha +9
Damage Vulnerabilities radiant
Damage Resistances acid, fire, lightning, cold; bludgeoning, piercing, and slashing from nonmagical weapons
Damage Immunities necrotic, poison
Condition Immunities charmed, frightened, paralyzed, petrified, poisoned, stunned, unconscious
Senses darkvision 60 ft., truesight 30 ft., passive Perception 13
Languages Common, Giant, Infernal
Challenge 13 (10,000 XP)

Innate Spellcasting. The wight’s innate spellcasting ability is Charisma (spell save DC 17). It can innately cast the following spells, requiring no material components:
At will: alter self
1/day each: counterspell, dispel magic, enlarge/reduce, spider climb, tongues
1/week: gate

Single-minded Purpose. The wight has advantage on attack rolls against followers of the fiend it is tasked to destroy and those in its target’s employ (whether or not they are aware of their employer), as well as the fiend itself.

Actions

Multiattack. The mask wight makes one Khopesh of Oblivion attack and one Enervating Spiked Gauntlet attack.

Khopesh of Oblivion. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 19 (3d8 + 6) slashing damage, and the target must succeed on a DC 17 Wisdom saving throw or some cherished material thing disappears from the universe, and only the target retains any memory of it. This item can be as large as a building, but it can’t be a living entity and it can’t be on the target’s person or within the target’s sight.

Enervating Spiked Gauntlet. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 19 (2d12 + 6) bludgeoning damage plus 11 (2d10) necrotic damage, and the target must succeed on a DC 17 Wisdom saving throw or gain 1 level of exhaustion. The target recovers from all exhaustion caused by the enervating spiked gauntlet at the end of its next long rest.

Wail of the Forgotten (Recharge 6). The mask wight emits an ear-piercing wail. All creatures within 30 feet of the wight take 65 (10d12) thunder damage and are permanently deafened; a successful DC 17 Charisma saving throw reduces damage to half and limits the deafness to 1d4 hours. Targets slain by this attack are erased from the memories of every creature in the planes, all written or pictorial references to the target fade away, and its body is obliterated—the only exception is those who personally witnessed the death. Restoring such a slain creature requires a wish or divine intervention; no mortal remembers the creature’s life or death.