Apparition
An apparition, in Interlife Earth, is a kind of ghost of twisted and distorted form, often incorporating claws and teeth or other natural weaponry into its shape. Apparitions are usually born of anger or frustration, divesting from people who die while under such strong emotions. On occasion, however, an apparition may form from a desire for vengeance or violence not from the decedent, but from his living relatives or acquaintances.
Distortions
The various ways in which apparitions are altered from their mortal forms are known as distortions. Many distortions involve the addition of appendages or other parts the apparition formerly didn't possess; apparitions may grow eyes or mouths in unusual places, or grow scales or armored plates on their skin, or sprout spikes from various locations. They may even grow additional limbs: extra arms or legs, or tentacles, or even tails or wings.
Distortions are not limited to the adscitition of extra parts or orifices, however. The alteration of existing parts is also common. Existing body parts may grow disproportionately large, with or without an accompanying change in shape; the nails and teeth are particularly prone to this alteration, the former growing into tearing claws and the latter becoming sharp and deadly. The form of the apparition may be altered in other ways, its joints turned backward or its neck or torso lengthened or its whole shape contorted into an asymmetrical parody.
While most apparitions retain enough of their original form to be recognizable, even if only as monstrous parodies of what they once were, some may be so refigured as to bear little or no resemblance to their mortal selves. Some apparitions grow bestial, looking more like animals or monsters than men; others may still look essentially humanoid in form, but nevertheless entirely inhuman. Some rare apparitions may have no fixed form at all, but become shapeless masses of ether, which may or may not sport various appendages.
Abilities
Most of the special abilities apparitions possess come from their distortions. Apparitions with sharp teeth or claws can use them effectively in combat, albeit only against other ghosts and ethereal beings, unless they manifest. Apparitions with wings may be able to fly even in the Spirit World where most ghosts are earthbound. Apparitions with oversized eyes may have better eyesight, and so on.
Some apparitions do, however, have abilities not directly tied to their forms. One common apparitional ability is that of fury; an apparition under particular emotional stress may grow temporarily stronger and tougher, though at the cost of some loss of control and of rational thought. Another fairly common apparitional ability is that of projection, by which an apparition can project onto other nearby entities their current emotions (usually anger), or the emotions they had at the time of their deaths (possibly fear). Some apparitions may share with certain shades the advantage of possessing a ghostly form of some useful object they had on them when they died, though this is much less common for apparitions than it is for shades.
Even aside from any specific abilities they may possess, apparitions tend to be among the most physically powerful of ghosts. This isn't to say that individual shades, specters, or wraiths may not be stronger than individual apparitions, but on the average apparitions are much stronger than any other major type of ghost, and easily able to overpower them in a straight fight—even without taking into account their distortional abilities.
Weaknesses
For all their physical strength, apparitions are fairly vulnerable mentally. This isn't to say that apparitions are stupid; like other ghosts, most apparitions retain their mortal intelligence, and there's no reason a very intelligent person may not arise as an apparition. However, apparitions generally suffer from an exploitable instability that makes them more likely to act irrationally during a crisis, and more susceptible to certain mental effects—not to direct mind control or possession, which apparitions tend to be rather good at resisting, but to more subtle manipulations of thoughts, memories, and emotions. (This is especially true of apparitions in fury, for whom rational thought is even more difficult than usual.) This can make apparitions in groups especially dangerous and unpredictable, since two or more apparitions who can project their emotions may enter into a sort of feedback loop that keeps building them to more and more extreme emotional states. Fortunately, apparitions rarely gather in large numbers, unless they all died together in a common cause.
Some apparitions go farther than this, and actually do lose their intelligence, becoming little more than unthinking monsters. These rogue apparitions may be treated by other ghosts as little more than beasts, though there are some ghosts who support better treatment of rogue apparitions, and even strive to find a way to restore their intelligence and bring them into ghostly society.
An apparition's distortions, too, may at times be at least as much a hindrance as a help. Great teeth and a long, sticky tongue may be handy in combat, but may make it difficult or impossible for the apparition to speak comprehensibly. Gigantic claws may make an apparition a deadly fighter, but prevent it from easily picking up or manipulating objects. More severe distortions may carry more severe handicaps; there are obvious disadvantages for an apparition who is quadrupedal, for instance, or who is so thickly armor plated that it hampers its mobility.
Psychology
Apparitions tend to be strong-willed, with violent tempers. How much of this is due to individuals having these traits being more likely to arise as apparitions, and how much is an effect of the arisal, is a matter of some debate. In any case, an apparition is very difficult to sway from its purpose, and some apparitions become remarkably single-minded. Apparitions have been known to position themselves as guards of a small area for years at a time, attacking anyone who comes near.
Not all apparitions, of course, are so obsessed as that. Many apparitions do integrate themselves into society and form normal relationships with other ghosts. Still, even those apparitions that serve a useful role in society do have a reputation for a fiery temperament.
Nonhuman apparitions
Apparitions arisen from creatures other than humans are very rare, perhaps because of their ties to emotions; beasts may have emotions in some sense, but not as complex and as strong as those of humanity. Nevertheless, some nonhuman apparitions have been sighted. By far the majority have been dogs, but the occasional cat has been known, and at least one bear apparition is known to exist. Many spectrologists have expressed their opinion that all of these nonhuman apparitions have arisen from the emotions and vengefulness of their owners, rather than their own, but it remains possible that some brute animals do indeed have sufficient emotions to arise as apparitions without any help from humans.
Though there are too few nonhuman apparitions known to form a sizeable sample set, it seems that most of the same possibilities that apply to human apparitions apply to nonhuman apparitions, as well. One unusual case is that of an apparition named Jubeo, a dog that has as apparitional distortions prehensile hands and organs of speech. So far, Jubeo is the only known nonhuman apparition to have developed such apparatus, and it's uncertain whether she's a special case or whether this is something that could in principle happen again.