Spirits are a tricky bunch, as there are so many variations on them, depending on region, religion, and even cause of deaths. So categorizing them is one of the most challenging aspects. However, the existance of spirits have been documented since the early ages, with some being treated as deities, and others being feared. In the early century, it was believed that being haunted by a spirit was a sign of your wrongdoings catching up to you, while others believed you had to lead the spirit to the afterlife. Depending on the energy of a spirit, they can perform different types of actions. While some may not be able to appear visably, they might have the energy to move objects, communicate, or in severe cases, harm individuals (scratching, burning, pushing, etc). Some even have the ability to possess, though, these spirits are not as common as others. The most common spirit most people will be greeted with, is the Poltergeist. An entity of a spirit who has low energy, but enough energy to move around objects to get your attention. It is believed that giving them your attention helps their energy grow, but documentation has not been strong enough to support that theory. Poltergeists can be lead into the afterlife using simple ritualistic steps, such as saging and communicating with them to let them know that they have passed on from this world. Wraiths are another common spirit, usually found with more energy than a Poltergeist. It is believed that once a person dies suddenly, they start off as a Wraith, as they take the apperance of what they looked like before they died. In most cases, they have enough energy to manifest, but overtime, the energy begins to dampen. However, if the case of their death is more severe, they could manifest into something a lot darker. (See: GHOULS, ONRYO) Ghouls are the next stage from Wraith, as if enough energy is manifested, they can devour bodies, flesh, blood, and other forms that contain a life essence, and grow even stronger. Though rare, they still make an apperance from time to time, relying on harming individuals in order to obtain more of a life essence. Their energy is strong enough to not only manifest, but also use more abilties in order to harm the living. Orbs are a bit trickier. While some believe spirits can radiate enough energy to appear as an orb, some also believe that it is due to a lack of energy that manifests the spirit into an orb, only appearing in video footage and pictures. Documentation is too different on the appearance of orbs, so further research must be done. The most dangerous of all spirits would be the vengeful spirit. Entities like Banshee's, Revenant's, and more commonly in Japan, Onryo's, have been documented as an entity that cannot be exercised. They cannot transition from the living world to the afterlife, due to their connection of anger, hatred, and vengeance. Do not, under any circumstance, try to encounter these entities without the proper equipment, or without the proper knowledge. I once read a report of an Onryo that managed to destroy an entire city in Japan due to his rage. Investigation of spiritual entities continues, as understanding their motivations can lead to safer interactions and potentially help in their transition to the afterlife.