Ghosts - Souls are easy to come by, and the vast majority of creatures - even monsters - have them. Godtouched and sentient animals have souls of great nuance and complication, and greater power than other living creatures. Souls that depart living bodies usually are bundled up into the astral sea and then processed in the demons' plane of Immigration.
Through magic or through sheer willpower, souls can resist this process and remain connected to the world of the living. They have created their own realm, an aforementioned inbetween that acts as an echo of material existence. When souls resist the call to pass on so strongly that they refuse to even enter the astral sea, afraid of the risk that they will be collected, they become ghosts. A ghost is a noncorporeal undead that remains permanently in the inbetween. Without the ability to dream, a ghost will quickly suffer the effects of sleep deprivation, and then, insanity. This will often warp a ghost's body, because astral bodies are based on the self-image of the soul. Ghosts are usually malevolent and cannot be reasoned with, due to their conflicting and chaotic senses.
Ghosts share several features: They are usually invisible, their astral bodies stuck in the inbetween. They can project themselves into the living world with effort, but this projection is invulnerable to normal weapons; normal attacks will only disrupt the ghost's concentration temporarily. Magical weapons can harm a ghost, as can spells and channeled energies. A ghost that is "killed" in this way has had its astral body disrupted. A soul without an astral body will usually create a new one, but with ghosts, their insanity often causes this to take years or even decades. Only an exorcism or psychic therapy can coax a ghost to leave permanently and join the afterlife.
Haunt - Occasionally the ravages of dream-deprived insanity will coalesce into crystal clarity in some ghosts. The ghost simply forgets it has died, and finds itself mindlessly repeating the actions it once did in life. These repetitions vary from haunt to haunt. Some haunts will simply repeat the same arbitrary action at the same time every night. Others will appear only once a year, and reenact the cause of their death. Because their actions are manifestations of the haunt's memories, a haunt will never attempt to communicate or acknowledge the presence of others. This usually makes them harmless. The exception comes when a haunt is able to possess the body of a living creature. Once possessed, a haunt will force its victim to reenact its death - which will often kill the victim. Groups of haunts are especially dangerous - reenacting ancient battles, with every new death adding to the strength of the group.
Ghast - An especially powerful type of undead, ghasts are ancient and have developed the power to manifest themselves in the real world on a constant basis. Their astral bodies have warped beyond recognition of their original form. They have gaunt, skeletal faces, a hovering hollow ribcage dripping with ectoplasmic viscera, and their arms are a sliding collection of of twisted blades. Their eyes are burning points of yellow light. They constantly give off a black poisonous smoke that can quickly kill people who breathe its fumes. Ghasts will kill anything that enters their territory, and they usually remain indoors or in poorly ventilated areas so their poison is more effective. Reports that they are sensitive to light aren't to be believed.
Flabberghast - A more powerful version of a ghast, a flabberghast's power and insanity have grown exponentially. They have gained powers that rival those of fey, and can easily twist and adjust reality around their victims. Actually less malevolent than ghasts, flabberghasts seem to enjoy tormenting their victims more than killing them. The hallucinatory insanity of their dreamless state causes them to warp reality to echo the chaos of their perceptions. On the rare occasions they show themselves, flabberghasts appear to be armless ghasts, with a skeletal face whose eyes and nose have shattered, and emit a very powerful burst of light.
Wraith - Wraiths are ghosts whose insanity is one of a dual nature. They sometimes resemble haunts, mimicking the actions of their past life. When confronted however, their astral bodies will contort and glow brightly, a white shimmering that obscures their features. Their attacks are usually melee - they will attempt to touch living creatures either through an extending arm or an arm shifted into a massive blade or tendril. Wounds inflicted by a wraith feel chilled, and drained. While their attacks do indeed cause physical damage to the body, what is far worse is that they absorb the life energy of those they wound or touch, growing stronger in the process. A wraith that has killed recently becomes an almost unstoppable creature from the momentum of its power that grows with every kill.
Will-o-wisps - Weakly powered ghosts who focussed on their ability to create orbs, will-o-wisps are generally more confused and in pain from their dreamless insanity than other ghosts. For some unknown reason, they most commonly are formed by those who have died by drowning. They seek aid, and while they still have enough faculties to recognize living creatures and signal to them, they either do not realize or do not care that those same creatures will soon become drowned themselves if they follow the will-o-wisps' light.
Specter - Perhaps one of the more psychologically disturbing kinds of ghosts, specters have not had their astral bodies twisted by their dream-deprived insanity. When they manifest, they appear just as they did when alive. Their insanity instead manifests in the behavior they undergo. They will stalk, hunt, and torture those that survived them. The pain of seeing departed loved ones reappear - and then attack, or say or do profane things can often drive grieving relatives even farther into the depths of despair. Many believe specters are demons masquerading as loved ones in order to toy with hearts. The horrible truth - that the identity is genuine - is usually more than most can bare.
Sluagh - Sluagh are ghosts that travel in packs. Their appearance tends to resemble gaunt and twisted human torsos, with very long hair and faint trappings of ancient robes. Their legs are twice as long as normal, and four times as thin; their legs flutter behind them in the sky as they travel. Sluagh are known to capture and detain the souls of the recently dead, keeping them from passing on to the afterlife and eventually forcing the soul to become one of them. Souls kidnapped by a Sluagh flock can be rescued, but usually with great effort; sluagh are swift and never rest in their constant migration.