Wraith

Wraiths are shadow-like, incorporeal undead capable of draining life from its victims an raising them as specters under their command.

Description
Wraiths typically have few memories of their lives as mortal creatures, if any, and often resent that which they enjoyed in life because of what they have since become in death.

Characteristics
Wraiths are full of negative energy, which animals often can sense. They can blight plants in their vicinity and extinguish small fires merely by existing.

Wraith are often resistant to acid, cold, fire, lightning, thunder damage and non-magical damage from bludgeoning, piercing, and slashing attacks, although silvered weapons can often overcome this resistance. They are also immune to necrotic and poison damage and immune to the charmed, exhaustion, grappled, paralyzed, petrified, poisoned, prone, and restrained conditions.

Abilities
The following is taken from the 5th Edition D&D Monster Manual, page 302.
 * Incorporeal Movement: The wraith can move through other creatures and objects as if they were difficult terrain. It takes force damage if it ends its turn inside an object.
 * Sunlight Sensitivity: While in sunlight, the wraith has disadvantage on attack rolls, as well as on Perception checks that rely on sight.
 * Life Drain: Wraith makes a melee attack against one creature. If hits, deals moderate necrotic damage. The target must succeed on a DC 14 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.
 * Create Specter: The wraith targets a humanoid within 10 feet of it that has been dead for no longer than 1 minute and died violently. The target's spirit rises as a specter in the space of its corpse or in the nearest unoccupied space. The specter is under the wraith's control. The wraith can have no more than seven specters under its control at one time.

The wraiths that Bells Hells encountered had the following additional abilities:
 * Enhanced Life Drain: In addition to the above ability, the wraith regains a number of hit points equal to the amount of necrotic damage dealt.
 * Tormenting Shadow: The wraith creates a sphere of magical darkness, which lasts until the end of its next turn. Creatures that enter the darkness or start their turn turn there must make a Constitution save (DC <15) against necrotic damage and having their speed reduced. On a successful save the creature takes half damage and their speed is halved.

Sword wraiths
Sword wraiths are undead who aspired to glory, but fell with no honor in battle. They now haunt their ancient battlegrounds. They are resistant to necrotic damage and non-magical damage from bludgeoning, piercing, and slashing attacks. They are also immune to poison damage and immune to exhaustion and the frightened, poisoned, and unconscious conditions.

Critical Role

 * On the Island of Viscan, two wraith inhabited cages in Opash's lab. During the Vox Machina's fight with Raishan, they attacked the party, but were ultimately scattered by the green dragon's Meteor Swarm.
 * In the Ruins of Thomara, Viskorad summoned two wraiths, attempting to delay Vox Machiana.
 * Lord Cioro, an individual of high station and importance in Ghor Veles. Lord's body found its final resting place in the part of the city that was caught by Vokodo's teleportation magic and transported to the island of Rumblecusp. The wraith-like entity, leading a swarm of ghosts, the Mighty Nein have encountered near the ruins of Ghor Veles might have been the Lord himself.
 * Bells Hells encountered three wraiths while Astral Projecting in a twisted mirror of Whitestone in order to disentangle the souls of Laudna and Delilah Briarwood. The wraiths appeared to represent Laudna's memories of being chased out of her various homes by fearful villagers who thought she was a witch.

Call of the Netherdeep

 * Eight sword wraith warriors guard a watchtower of Cael Morrow under the leadership of a sword wraith commander named Beltreath. They are former defenders of the city who fell during the battle against Gruumsh and, as of 836 PD, protecting the ghost of Hadarai.
 * In the Grottoes of Regret in the Netherdeep, when entering a Haunted Ashes locations, an individual is forced to relive Alyxian's memories of his allied soldiers, who aid him in the battle against Torog, pillaging the village, they previously saved. In his memories, the soldiers take form of four sword wraith warriors led by a sword wraith commander named Kalagothe.
 * In another Grotto of Regret, Alyxian remembers the battle at the Betrayer's Rise. The hordes of his enemy, Torog, take form of sword wraiths.

Other

 * As a part of the "Shard of the Shadebarrow", an adventure hook for both the Tal'Dorei Campaign Setting and Tal'Dorei Campaign Setting Reborn sourcebooks, a wraith claiming to be the spirit of Avandros was active in the Shadebarrow, where it had animated an army of ghouls and ghasts and conquered the Silvercut Crossroads.
 * In of The Legend of Vox Machina, Delilah Briarwood called upon wraiths to attack the Greyskull Keep and Vox Machina who stayed their. They took out a handful of Tal'Dorei guards, keeping watch over Vox Machina, and extinguished the lights along their way. The defenders were unable to physically harm the wraiths. The guardian captain named Jarett Howarth lit up a torch, revealing that light weakens the wraiths, which helped Keyleth thought of creating a bright sunlight, successfully bringing the fight to the end phase.
 * In Critical Role Delilah summoned two invisible stalkers to attack the keep with probable reason of eliminating Desmond Otham, a source of Vox Machina's information of the Briarwoods' operations in Whitestone.

Trivia
The plane where Bells Hells encountered wraith-like entities, a twisted version of Whitestone that Delilah Briarwood inhabits, is similar to a Domain of Dread as described in Van Richten's Guide to Ravenloft. These domains are innumerable, isolated demiplanes within the Shadowfell that each imprison an evil villain, called a Darklord. Each domain mirrors the Darklord trapped within by drawing on their crimes, failures, or impossible ambitions and twists their desires into ironic torment, to the point that the Darklord hates the domain. At the same time, the Darklord is the root cause of all suffering within the domain and has considerable influence over it.