A Grey Reaver is a particularly rare and terrible form of undead, born from the combined horror, fear, and suffering of an entire city or race being slaughtered. Only the most horrible atrocities, where the streets run red with blood and the air is filled with the screams of the dying, can birth one of these horrid abomiantions.
A Grey Reaver is a nightmare assemblage of rotten flesh and shattered bone, held into a roughly humanoid shape by the raw force of the energy that animates it. Despite the roughly human size of the thing, it contains fragments of every creature that died to give birth to it, giving it a density and longetivity far beyond that of more common undead.
The head is little more than a rough lump of grey, rotten flesh, with a gaping maw lined with splintered bones for teeth, and a pair of sickly green flames dancing in charred holes where eyes should be. It bears with it a charnel smell, powerful enough to spook animals from a good mile away, if upwind of them.
The most enduring memory of survivors, however, is the thing's voice; it can speak, even eloquently, depending on the spirits that animate it; the sound is a horrific mixture of their dying screams, modulated into words as it pronounces doom upon those it encounters.
A Grey Reaver exists for but one reason: to take vengeance for those spirits who comprise it, by hunting down and slaying those responsible for their deaths. This can extend far beyond those who slew them, and Grey Reavers have been known to hunt down politicians and merchants whose role would appear, at a glance, to be little more than incidental - although careful examination always finds some act or policy that the victim was behind that drove the slaughter to happen. Worse, if a victim escapes the Grey Reaver into death, it will turn to fixate on those of the dead person's lineage, hunting daughters and sons who are, most often, completely innocent.
A Grey Reaver appears to be little more than a killing machine, hunting down and butchering those responsible for it, often using hands tipped with jagged shards of bone to rend their chosen victims into bloody ribbons. Were this all, the abomination might be seen as justifiable; instead, each person slain has their own spirit consumed by the ragged maw of the creature, even as some of the original aniamting spirits slip away. In the end, when all that is left are the spirits of those slain by the creature, it settles into a heap of putrefying flesh, to hold those captive souls in torment forever, if it is not cleansed.
This final form is often the cause of areas considered blighted and unholy, as the anguish of those consumed stains the surrounding lands; long after the heap has decomposed, the spirits remain bound to the spot, wailing their eternal suffering to deaf gods.