What Happens to ghosts as they linger?

As the years turn into decades, turn into centuries, a ghost will generally see their abilities atrophy if they cannot exercise their abilities as an incorporeal being. Abilities that a ghost can use like Alertness, Empathy, Subterfuge, and the like tend to rise. Ghosts that linger on a very long time usually pick up derangements. When a ghost develops a new power, they usually pick up a new handicap to go with it. A list of powers and handicaps is at the bottom of this threads.

Finding Eternal Rest: In writing fiction and playing out RPGs, it can be a very satisfying story to help a ghost find its eternal rest. A ghost that resolves his or her lingering goals, or is convinced to simply let them go, passes on to the normal afterlife non-ghost souls get (which I’m still working on). This is common knowledge, even among most peasants. Most ghosts are actively trying to pass on to the afterlife.

Finding Oblivion: A ghost that is destroyed by magical attacks or another incorporeal creature faces oblivion, nothingness. In very rare cases, strong willed ghosts can will themselves to regenerate after facing seeming destruction like this, but they are virtually guaranteed to come back disfigured, insane, or sporting some new ghostly Handicaps. Most ghosts fear being reduced to nothing and resist this with every fiber of their being, but some ghosts give up and actively seek to end it all.

Finding an Eternal Vigil: Sometimes, a ghost decides that she likes being a ghost more than she liked being alive. Ghosts like this are rare but they are very powerful since their Willpower often grows over time. This most often occurs when a ghost’s unresolved business is continuous and ongoing. If a ghost is lingering because she wants to look after her orphaned son, the ghost will probably pass on when her son grows up to adulthood and finds a steady livelihood. A ghost in this category instead decides to linger on to protect and guide her grandchildren, great grandchildren, etc in perpetuity.

Becoming a Poltergeist: Sometimes a ghost fails to achieve his goals and does not make peace with life as a ghost. At the same time, the ghost fears being reduced to nothing and still actively resists oblivion. Ghosts in this category are irredeemably insane as their former passions and drives turn into neuroses. A ghost motivated by greed may dedicate its entire existence to guarding a single gold coin or something similarly petty. They basically are monsters now that either haunt a single area and lash out at the living out of spite, or they are roaming monsters that go around spreading suffering randomly. A poltergeist may haunt his old family home (or the site where his home once stood) violently repelling all intruders long after his family line was extinguished.

Becoming an Astral Spirit: If ghost avoids madness and oblivion but gives up on his original obsession, or is now incapable of resolving it due to outside factors the ghost will eventually be drawn to the astral plane. This is especially common when a ghost really revels in using her ghostly powers, but for general amusement and not to pursue her ambitions left over from life.
I’m still working on the finer details of the Astral Plane. Currently I’m envisioning Astral Plane is a realm of pure thought with little emotions. An astral spirit is basically an avatar of the ghost’s powers and aptitudes without the person’s original personality. They are virtually unrecognizable as the person they once were, even more so than a poltergeist. Eventually no trace of their original identity remains, but they still technically exist.

Becoming Ensnared by a Necromancer: This is not healthy for a ghost. Depending on the nature of the ghost’s imprisonment, they might be metaphorically and literally worked to death and face oblivion; they might be driven mad and become poltergeists, or they might lose their identity and get sucked into the astral plane.
I am still working on the details for how necromancers can command ghosts. One dot powers let a necromancer find nearby ghosts. An uncharacteristically nice necromancer can even bargain a mutually beneficial goal, "You do me this favor and I'll do you a favor." In most cases, ghosts can not do much if the necromancer or medium is lying.
Magic users need four dot powers to restrain or issue temporary commands and five dots powers to permanently enslave ghosts. Even a weak willed ghost will fight a necromancer much harder than a standard zombie or wight, so many necromancers don't bother with ghosts at all.
It's fairly easy for a necromancer to use ghosts as a spies. A powerful and wily necromancer might command a ghostly assassin, but even the most powerful necromancers in Scarterra cannot command an army of ghosts.