Wraith is a Scottish dialectal word for «ghost» or «spirit». In Dungeons & Dragons, they are undead creatures first introduced in the «white box» set (1974), where they were described as high-class wights with more mobility. As restless apparitions they are, wraiths lurk in the shadows, thirsting for souls. Those slain by one become free-willed wraiths as hateful as their creator.
Infused with the necromantic essence of the Shadowfell, a wraith is a spirit bereft of soul and body: a hollow vessel containing minimal personality and knowledge, if any. It usually remains near where its physical form fell or was buried. The touch of a wraith usually causes weakness. A mad wraith weakens the mind instead of the body, and its touch can even drive a creature to attack its allies.
A wraith is an incorporeal creature born of evil and darkness, despising light and all living things. A wraith drains the constitution from living creatures, turning them into new wraiths upon death. A wraith is powerless in natural sunlight and will flee from it. A wraith is always lawful evil. A wraith appears as a sinister, spectral figure robed in darkness. It has no visual features or appendages, except for its glowing red eyes.
When a wraith slays a humanoid, that creature’s spirit rises as a free-willed wraith of the same kind. With the aid of magic or ritual, and with the proper components, a necromancer can summon or even create a wraith. Other wraiths are born on the Shadowfell, and many remain there or enter the natural world through planar rifts and gates. When many people die abruptly, a dread wraith can coalesce from their collected spirits. Common wraiths can also evolve into larger, more malevolent wraiths over time.
In the «Sharn: City of Towers» supplement (2004), we’re introduced to the forgewraith. Haestus d’Cannith was the overseer of a creation forge in the former nation of Cyre near the border of Darguun. Killed before the Day of Mourning, Haestus was risen by the mists and transformed into a forgewraith. We can tell forgewraiths are the unfortunate result when a humanoid meets his or her demise due to intense heat, like a lava pool, or an arcane-tempered fire, like the various House Cannith forges. Some forgewraiths may actually be made up of multiple weaker spirits.
Forgewraiths are shadowy, smoky undead figures, outlined in fiery red. Fire burns brightly where their eyes once were. Those eyes lock on any living creature with a fiery hatred. As incorporeal undead, there is a chance that weapons pass harmlessly through them. Born of fire, forgewraiths project a fiery ray at their victims, hoping to engulf them in fire like they had once been; just as with regular wraiths, a humanoid slain by a forgewraith may themselves become a forgewraith.
In your campaign
A wraith uses hit-and-run tactics and flanking to gain some sort of tactical advantage, phasing through walls, doors, and other obstacles to break line of sight. When heavily damaged, the wraith flees, only to return after it has regenerated most or all of the damage suffered.