And here we have another Eclipse: The Codex Persona question:
How does the Witchcraft Power Possession in the Path of Spirits work? Assuming it is fully upgraded, Is it just a (DC 13 + Cha Mod) will save or die with the unlimited duration modifier? If the witch ejects the old soul, what happens to his/her abandoned body? What if someone attacks it? What if the witch in the new body dies? Are any of the versions dispelable or reversible?
The basic Possession power puts the user’s body into a coma – an effect easily mistaken for brain death – but the user’s spirit remains linked to his or her original body. Dispelling the effect (or allowing a new save, or performing an exorcism, or applying similar powers) is quite possible, and will return the user to his or her original body. If something happens to the user’s body, or it simply remains abandoned long enough to slip into death (I wouldn’t worry about this unless something is already gravely wrong, conditions are very bad, or the user stays out-of-body for more than a day or two), the user will die with it. Removing the maintenance cost will not change any of that, although it does make possessing someone for hours far easier.
Adding the ability to abandon the user’s original body does change things. With that modifier the user may opt to break his or her link with his or her original body and establish a link to a new one, displacing the original owner. This usually does kill the original owner – unless, of course, they happen to have some ability to astrally project, become a free spirit, navigate the dimensions on their own, use their body as a sympathetic link to act through (well, technically they’re still dead, although it may not hinder them all that much), opt to become a ghost, or have some other means of acting while disembodied. Displacing someone’s spirit like this and stealing their body is a grossly evil act of course – it is, after all, considerably more personal than a rape-and-murder – but that’s why this sort of stunt is usually reserved for villains.
Unlike a spirits link to the body it was born in, a possessors link to his or her new body is artificial. It can be dispelled, the spirit is subject to exorcism, and so on. An opponents success in such an endeavor leaves the user bodiless (since they’ve voluntarily and intentionally given up their link with their original body) – and thus subject to the same fate as the original owner; passing on unless they have some way to hang around. Of course, even that may not do them much good if the people doing the link-breaking can disrupt or banish their astral forms.
Now if someone gets possessed, and the possessing spirit is driven out, then you have a living (if empty) body – and calling an unresisting spirit from the outer planes (or even just from the near astral if you’re prompt about it) is not much of a trick; Monster Summoning I can do it and so can anyone capable of holding a seance, whether by magic, ritual, or psychic talent. Now normally such an effect can only anchor a spirit for a little while – but if said spirit has it’s own living body handy, it can usually move right back in with relatively little trouble. (Shamans traditionally retrieve wandering souls and return them to their bodies quite routinely).
If someone does want to use this as a save-or-die offense… It’s possible (if of rather short range), but they’d be very well advised to invest in a pile of Immunities to various methods of driving them out of their new body or (preferably) learning methods of surviving as a free spirit. A villain who has done so (and has probably also invested in Opportunist/Gets to make a free transfer attempt at the point when they’d normally die) makes an excellent reoccurring opponent though; he or she is not likely to target the PC’s – such characters all too often make their saves, get rerolls, or have defenses – but taking the body of some convenient hostage, child, or other bystander is a great way to come back again later.