Wraith

Wraiths (生霊) are low-tier undead.

Appearance
A Wraith resembles a black ghost with a wailing expression.

Abilities
Wraiths specialize in stealth, using it in both offense and defense. Wraiths had astral bodies, and so they could move straight through walls and other such obstacles. Still, there was a limit depending on how thick those walls were, so it was hardly unlimited, but the thickness of the room’s walls were no problem for it.

Based on the Web Novel, they might be the ones who could pass through walls and had a specialization of hit and run tactics. In other words, the possibility is high that they can deal damage by negative touch.

Trivia

 * A Wraith was summoned by Ainz Ooal Gown during the E-Rantel Cemetery Incident while saving Nfirea Bareare, to halt any interference from other adventurers.
 * Wraith did not appear in the Anime, only in the Manga and the Light Novel.
 * According to Neia, Wraith would take the shape of the species who saw them.
 * During the campaign to liberate the Northern Holy Kingdom, Ainz summoned several undead called High Wraiths.