Despoiler

In the ranks of the Unborn, blood runs thin and corrupted by the stain of the Black Forest. Some individuals, however, carry with them more of their misbegotten lineage than others.
  These disfigured harbingers are known to those not of their cult as Despoilers, a name fitting of their purpose.
 

Thieves of Hope

Unlike most agents of the Congregation of Witnesses, Despoilers have little interest in veiling their true nature when they prowl the streets of the city-states during moonlit nights, openly and proudly displaying their deformities for all to see.
  Those unfortunate enough to encounter these monstrosities will invariably be embraced by them, and in the process they will be preyed upon. One or more probosces, long and flexible, often adorns the hideously warped faces of the Despoilers, which they use on their hapless victims. These appendages, using any passage they can find, worm their way into the brain of the victim, whereupon they will begin to suckle.
  But instead of draining blood or cranial fluids, this predation is far more sinister. The Despoiler is interested only in positive emotion. Memories of joyous moments, of cherished loved ones and the small joys of life. It is these things that are drawn and consumed. Of particular interest to the Despoilers is the memory of the Eternal Hymn, which they will erase with glee.
  As if this was not enough, the next step is what has earned these creatures their name. Just as they ingest positive psychic energy, they vomit out negativity. Depression, anxieties of all kinds, worries over trivial things, paranoia, psychosis and other ailments of the mind. All these things and more the Despoiler regurgitates into the minds of its victims, who are none the wiser that such an encounter had ever taken place, as the Despoiler makes sure to suck up the memory of it, too.
 

Bigger Picture

It is tempting to simply call the Despoilers monsters preying on the underbellies of human settlements and be done with it, but the truth is that they have a very specific purpose in service of their Tyrant master. It falls unto these abominations to destabilize and demoralize the populations of the city-states so that they become discontent with their lives in their walled cities.
  Sowing discord and grief alone is probably a pleasure for the Despoilers, but the ultimate goal of these efforts is to drive humans away from their faith and, more importantly, what their faith demands of them; the perpetuation of the Eternal Hymn.
  The Despoilers could be seen as a natural, subtler continuation to the undermining efforts that began with the Unveiling. Instead of violent uprising, the Despoilers are an insidious, silent cancer that gnaws at the seams of society.
 

Preventive Measures

Since the Despoilers erase the memory of themselves from their victims, it is exceedingly rare that anyone should even know that they exist. Only those victims whose predation was interrupted for one reason or another have any recollection of these beings, and even then it is rare that authorities take their frightened ramblings seriously.
  However, there is an unlikely organization that has risen to the occasion. Owing perhaps to its disseminated nature, the order of the Mageslayers has successfully tracked and slain several Despoilers.
  Their charms of Deadwood seem to have a dampening effect on the capabilities of the creatures, suggesting that the Despoilers may have a connection to or make use of the Tapestrum Arcanum in some way.