The Possessed is a term describing when a person's personality, their very soul, some would say, is suppressed by a psychically powerful entity from the Great Beyond. Most often it is the Infernal beings that have the wherewithal required for this, but on rare occasions the spirits of mortals can do it as well. Those ghosts that can possess the living as a rule were not the nicest people to begin with. As usual though there is not hard set of established guidelines though in the Crawlspace universe.
An incorporeal being walking around in our world is similar to someone that would take the bus to the store making his way Mars. Things on the other side are meant to be there, some serious metaphysical dynamics are going on when it does occur. It really isn't a jog in the park being a demon banished from this plane of existence. The person possessed by a spirit is not only the harbinger of gory scenes about to happen but an offense against the ways of nature. And they usually bring all of their supernatural powers with them when they come to visit.
The would-be possessor requires the cast member under spiritual attack to fail two consecutive Nerve Draws each time it can wander upon the sands of our world's hourglass. The demon, or malignant spirit, is then assigned through a random Draw (Ace= One...King =13) a certain of points. The points equal how many Draws it can make before being forced back to whence it came. While on this mortal coil, with each failed Nerve Draws the Possessed can cause among Characters, it gains an additional Draw. Once all of the available Draws have been used up, the invader returns back to the Great Beyond and re-start the possession all over again. Many times demons would just rather kill their host and call it a day before all is said and done.
Though there is no real set way of expunging the not welcomed entity, the "Exorciser(s)"of the Possessed is guaranteed one Fame card for deciding to be so. The Player though has to decide whether it is going to be used during the play session, err filming, or stored on their Resume. How a possessing spirit is exorcised from this plane is up to the GM, though he or she, should be familiar with the "Learning the Name" ritual magick, on pg 26 of the rules book.