ghost

A ghost is the soul of a creature which has failed to move on to the afterlife after death. Ghosts are rarely benign, angrily attempting to finish its business in life and pass on to the next world. Those who linger in the world of the living too long will transform into demons.

Origin

Most souls peacefully move on to the afterlife when they die. Sometimes circumstances do not allow them to depart the world of the living and they remain behind. The most common way that ghosts come to exist is when a person dies in a sudden, unexpected, or violent manner. If the person has a particularly strong will and some unfinished business, strong desire, or lasting regrets, they can remain in the world of the living. At this point the soul exists as a ghost: an intangible, invisible creature that appears identical to the person when they died.
Occasionally, other means bind a ghost to the mortal world. Some powerful magics can tether a soul to a location, preventing them from departing even though the soul wishes to. Thankfully, such magic is rare and few intentionally use it.

Fate

The ghost will attempt to resolve whatever it is that leaves them tied to the world, such as gaining revenge on their killer, protecting a loved one, or severing the magic which binds them. If they succeed, the ghost will be able to pass on peacefully, departing to the afterlife as normal. Due to their limited ability to interact with the world, however, most ghost find themselves frustrated in their attempts. Over time this frustration grows, especially as the spirit lacks the ability to grow or learn from its mistakes without a body, remaining perpetually in the same heightened emotional state that caused them to remain a ghost. Eventually, this frustration overwhelms them and the ghost transforms into a demon, their individuality forever lost.

Abilities

Ghosts possess very few ways to interact with the mortal world. They retain any skills and knowledge they had in life, but are unable to actually physically interact with material things. Mages and other users of magic are able to cast spells, though the inability to manipulate any material components prevents many of them from working. Additionally, except for extremely powerful individuals, they can only cast most spells once before they lose the ability to do so, lacking the ability to rest and regain their arcane energy and focus. Those with psionic powers are luckier; their minds continue to exist, allowing them to interact indirectly with the world. This allows psychic ghosts the ability to move on relatively quickly.
Ghosts can interact with the living world through some means, however. Those who were close to them in life can hear them, though it comes through as a soft whisper from a great distance, the words often difficult to make out. Many believe themselves to be imagining it. Ghosts can also manifest themselves in dreams, causing a vivid experience for the dreamer. These dreams fade as normal when a person awakens, thus often only bits and pieces of it will be remembered.
Ghosts can additionally cause minor effects on the world, such as causing a room to become briefly chilly or hot, create small movements in light objects such as knocking paper around or banging two pans hanging on a hook together, or extinguishing candles. They can write short messages, typically one or two words, on certain surfaces, such as a mirror or window covered in steam, a puddle of blood, or thick dust. Finally, they can create small amounts of ectoplasm, about a cup or less. Any of these actions causes tremendous strain on the ghost and most are unable to do more than one or two of these things a day.

Dealing with Ghosts

For the most part, a spirit will be nothing more than a minor annoyance for most, eventually transforming into a demon and transmigrating to Hell. However, for some they can cause distress and pain, and others wish to prevent a demon from forming.
Ghosts can be seen and communicated with through a variety of magics, allowing their needs and desires to become known. Speaking with a ghost isn't easy, as they tend to be fairly single minded and are not able to remember things more than a few hours old. The longer a ghost has lingered, the more frustrated and incoherent it becomes as well, making communication difficult. If a medium can determine what it wants, fulfilling its desires can cause it to move on to the afterlife.
More frequently, a ghost must simply be exorcised. The exact mechanism for this depends on the rules of the afterlife the ghost will be sent to, but typically involves a ritual performed by a priest. The ritual often gives the ghost more ability to interact with reality, or at least to utilize all its reserves to do so. Ghosts typically do not want to be exorcised, as doing so means whatever desire holds them to the mortal world will be unfinished. This makes an exorcism a dangerous task, one not for the faint of heart.
Ghosts who have been sent to the afterlife do not remember much of their time as ghosts, mostly just having a vague sense that something went wrong and expressing generalized contentment if they succeeded in their goal or mild disappointment if they didn't.

Type

Metaphysical, Divine