Cairn Wraith

The Reaper Cometh... with a square base.

The Cairn Wraith is a ghost unit used by both the Vampire Counts in Warhammer Fantasy and the Nighthaunt in Age of Sigmar.

Age of Sigmar

Amongst all the assorted spirits of the Nighthaunt, you have to be a special kind of sick and twisted bastard to become a Cairn Wraith. That may sound meh due to the sheer quantity of them present in the setting, but it is indeed true; when, say, a really spiteful mass murderer goes to the underworlds of Shyish, they won’t quietly fade away. Instead, all aspects of their personality get thrown in the garbage except for their sheer, burning hatred, which is weaponised by the processions to Rip and Tear their way through any mortal that gets in their way.

Interestingly enough, because they were one of the original Nighthaunt units before Soul Wars, they apparently all used to be lone-wolf style predators, hanging around near gravesites and such, as well as occasionally joining a Vampire or Necromancer for shits and giggles. This changed after the Necroquake, with it being explicitly said that bone daddy bound ALL of them into his service with something called “The Great Cairnoch”. Whether this was some impressive building or just another plot-related macguffin in unknown.