Taken from the research notes of Mr.Shade, famous necromancer and ectomancer.
-----The Types of spirits-----
The restless dead
The first thing to understand about the spirits of the dead is that they come in three variety; Ghosts, Wraiths and Specters. Another thing to mention are flatliners and ghostwalkers
This type of spirit is technically not one at all, it is merely the psychic and emotional remains of a tragedy or someone's passing. Ghosts posses no form of intelligeance or free will. They are the most common type of spirit encountered, composing around 90% of spooks, 8% Decorporated humans and only about 2% are the other type of spirit.
A wraith, is the actual spirit of a dead person that roams the world, almost all of them are in the afterlife and very few comes back or stay here long. Wraiths are generally bening as those who aren't become specters fast.
Very few things are scarier than specters. Specters are the wraiths who have given in to their madness or negative feelings, twisting their soul into something that can be described as anti-life. Specters feed off those feelings and so prey on mankind for energy.
Unlike the previous entries, these are still living persons that can leave their body and become pure spirits.
Flatliners are a new type of ghostly entity, it consists of people in a coma that are thrown out of their body, they are the source of NDEs. However some rumors float around that some groups are working on recreating this effect but in a controlled manner.
Ghostwalkers are those who may via meditation separate their physical and spiritual self, many shamans were ghostwalkers. It is unknown if any may become ghostwalkers or if it is an innate gift. ((From the books; Lucas Tanner)
The second classification of a spirit is his mode of operation or form. There are six known forms; Poltergeist, Banshee, Wisps, Mindflayers, Skinriders and Avengers
These spirits are those who's driving negative emotion is anger and a feeling of betrayal. They posses the ability to manifest physically and perform minor supernatural feats. Avengers will attempt to correct the wrong made to them often violently. They are bound to the place of the Crime and have a rather thin range of action.
This type of spirit is born of jealousy and manipulation. Banshees may speak ghostly whispers, force feelings into their victim's heart and send nightmares. Banshee normally cannot manifest physically. Their most recognizable trait is the wail of anguish they give when feeding. (( Marriane))
Nothing is more sick than a mindflayer, they are spirits driven by insanity and cruelty. They delight in causing pain. They may take a physical appearance and have the ability to mentally assault and scar their victims. All Mindflayers are specters or flatliners.
Their most recognisable trait is their horrid appearance. ((Carlos))
These spirits are one of the most common and are driven by feelings of territoriality and greed. Poltergeists may manipulate items and throw them however they cannot physically manifest. Poltergeists cannot under any circumstance leave their homes. Poltergeists are most often ghosts.
These spirits are bound by desires of domination and superiority. They may temporarily posses someone's body and make it move according to their will. They are often responsible for rumors of demonic possession. Thankfully, these spirits may only posses nervous or weak willed people and cannot cause self harm to the body they posses without being driven out by survival instinct.
These are born from feelings of loneliness or abandonment. They are known to manifest as glowing lights, strangers in need or other things to entice victims to follow them. They are able to affect their environment as to create traps for their targets.
-----Fighting the dead-----
Every types have their own weaknesses. Ghosts are rather easy to dispatch as sunlight destroy them if not in a protected location or object. Iron and salt banish them back to their fetters to rest.
Wraiths and specters cannot be destroyed as their soul are immortal. They can however be damaged or banished. Salt will burn them, sunlight will cause pain to a specter and so will iron. Rumors say a specter can devour another spirits but this is unconfirmed.
Projectors can be wounded in the same ways and be effectively killed. It is important to note that killing a projector will kill the person and his or her body.