Greetings once again!
Of all the fates that can befall a traveler, perhaps none are more terrifying than transpossession. Many a wizened scholar is aware of the influence of the so-called "Dark Powers," the mythical insidious forces that sometimes take a secret sinner into their arms, rewarding the hidden crimes while simultaneously punishing them in turn.
Transpossession is a different sort of corruption entirely. The experienced explorer is no stranger to demonic fiends; from somewhere beyond the Mists, the most depraved conjurers and diabolists are able to summon infernal beings bent on the corruption and destruction of mankind. What is not as well known is that these same entities are capable, on rare occasions, of reaching through the Mists of their own accord.
When a soul of sufficient dark potential piques their interest, these abyssal beings begin whispering in their subject's mind in subtle ways; over time, as the subject heeds the creature's advice and sinks ever deeper into damnation (a fact they often overlook in light of the perverse gifts their 'benefactor' bestows on them) the voice grows more overt and insistent. Eventually, the victim succumbs completely to the invader, who takes their place within our world and casts their host's soul into the hell from whence the interloper came.
Through long study, I've managed to identify five of these fell entities that are particularly insidious to deal with, and the methods they might use to ply their victim's weaknesses.
Typically associated with women (the much rarer male variant is called an incubus), the succubus is one of the most common demonic presences encountered. They play on their victims' senses of insecurity; seduction is the bread and butter of these creatures after all, and instructing their hosts in these arts is often all they need to gain a toehold in the life of their target. Once such powers of manipulation are in their hands, the sinner can be tempted towards ever crueler uses of their newfound power.
The most likely targets for such creatures are those who live within the shadow of the desirable and glamorous, and who consider themselves drab or uninteresting by comparison. Alternately, the mortal may be someone who views their life as dull and tedious, and is susceptible to the idea that clandestine trysts and sensual manipulation carry a dark, desirable romance.
Loathsome and vile in the extreme, the uridezu is a rat demon, who delights in spreading pestilence throughout mortal realms. Most commonly found in densely populated urban areas (commonly found in parts of Nova Vaasa, Dementlieu, and especially Falkovnia), these fiends grant insight into diseases and their spread, as well as power over rats and other rodents. In an especially dense metropolis, the ability to control rats can often bring a person sudden wealth, as they find themselves in control over an abundant and renewable food source.
Victims of the attentions of an uridezu are often destitute or plague-ridden. Their circumstances are so pathetic that their are willing to take any assistance, even from an infernal source, if it means elevation from their tribulation.
Emaciated, jackal-headed fiends in their true form, these fiends are scavengers in nature as well. Law and lore are their stock in trade, and the more forbidden the knowledge, the better. Often, they don't even need to tempt their intended hosts with any abyssal powers--the dark knowledge they bring is frequently more than enough to tempt their victims onto the path of damnation. Should their vast breadth of lore prove ineffective, they are also masters of the arcane, and more than willing to tutor a foolish mortal if it will bring them one step forward to taking the mortal's place.
Obsessed scholars may seem like the most likely target for an arcanoloth, and while such individuals are indeed in danger of this fiend's attention, a far sweeter target is the sage who is in over their head, who has pursued or boasted of mastery they have not achieved (or are incapable of achieving). The devil can then offer the target a way out (to the luckless mortal's eye, the only way out), allowing them to save face and advance their career, while giving the demon the footing they need.
Even in the diabolic realms, there must be order. Osyluths serve as some form of fiendish constabulary, and while they rarely initiate transpossession, they are noteworthy because of the vast damage they can do on those rare occasions. They offer their victims a keen insight into the human psyche, an ability to predict what others will think and do, and a suite of magical abilities which ideally augment lone lawmen.
Targets of an osyluth's attention are invariably some form of police (very rarely, they are lawfully minded vigilantes adrift in a large lawless population) who are overwhelmed with the chaos and evil they must face on a daily basis. The osyluth's assistance is accepted because unlike other fiends, in the beginning they actually are doing good. Inevitably, however, the osyluth convinces the target towards more merciless interpretations of the law and their mandate to enforce it, until the damned is no better than the scum he sought to curtail.
Of all the fiends in all the hells in all of existence, there is none I fear more than the jovoc. If there is anything that the jovoc embodies, it is spite: the vinegar of the blood that causes a man to live for nothing but pure malicious bitterness, willing to sacrifice themselves if it means harming those who have crossed them. To targets who feel powerless against those who have wronged them the jovoc offers the means, motivation, and expertise to seek an endless, unbalanced revenge. Those deep within the jovoc's thrall even gain the jovoc's most dangerous ability: the power to inflict any damage done to them on everyone in their vicinity.
Those susceptible to the jovoc are the downtrodden people who recognize their low lot in life but are unable to recognize their own fault in it. Instead, they seek to blame everyone around and above them; anyone who is happier, wealthier, or more powerful than them becomes the enemy no matter how little they've done to the victim. They seethe with resentment towards their fellow man, but are impotent to do anything about their feelings. Until they hear the first whisper, of course.
To conclude: transpossession remains a remarkable rare occurrence, a fact for which we can all be thankful. However, should you suspect such a phenomenon, I highly recommend you consult your copy of Van Richten's Guide to Fiends before engaging such a powerful enemy. Hopefully this missive will give you at least an inkling of how to identify the most likely (or dangerous) culprits in such a scenario.
Wishing you all the best,
Frankie "Farshot" Drakeson, Lord Mayor of Carinford-Halldon
Jim Stearns is a deranged hermit from the swamps of Southern Illinois. His mad scribblings can frequently be found in Quoth the Raven, as well as anthologies like Selfies from the End of the World, by Mad Scientist Journal.
I am become death, destroyer of worlds.