What I was taught about intangible beings.

One thing, don't believe everything you read from the bible. It has been heavily tainted by the hand of power hunger evil men. What I learn from my mother about the paranormal came from her grandmother (on her father's side) and grandfather ( on her mother's side). They were raised as christians but became something different later. They encounter all kinds of supernatural events. By these encounters came their knowledge.
When someone dies, your core of your being leaves this plain but your memories stay here. They were created on this earthly plain and are recycle to the next generations. Some evil beings use these loop hole to cause troubles for the living. This is the main reason why not to use ouji boards and seances to summon the dead. It is not a sin to talk to the dead that is already hanging out at a site.
Ghosts as you know come in different forms. Residue haunting is a place that has been stain by the memories of the living. This type of haunting is harmless. A low level haunting is the intelligent memories of a soul which core has left this plain. It is very weak and must take time to gather energy to manifest. A medium level is that a the core with its memories intact and isn't aware its physical body is gone and are confused. This types of spirits can be awaken to their situation and most of them leave this plain. A high level is very extremely rare. These spirits are on a mission. They have mastered some abilities to affect the surrounding environment. Most are evil and can be mistaken for demons. Kind ones rarely reveal themselves to the living and usual protect a certain area or person.
Non-human entities. Low level beings are single animal spirit or transdiminsional parasites (poltergiest). They are mostly harmless but mostly annoying. Medium level are shadow beings which are larger intelligent parasitic beings that attach to people and cause illness. Sacred site guardian is a group of animal spirits that combine to form one being to watch over feeding area or water hole. Possessers are evil beings that love to cause chaos to the world of the flesh. It takes time for them take over a person. They are low level evil entities (demons) and are mistaken for fallen angels of legend. Doppelgangers are parasitic race of very common tricksters. They take the form of living and the dead. They can download memories from the victims though a type of psychic scan. Their form can fool 95% of psychics and 99% of the living. Only the eagle eyed can tell the difference. High level are extremely rare and dangerous. Most are found in rural and dark dwellings away from man. Others are summoned by true masters of a craft. And others are NEVER noticed by anyone because they keep to themselves. These DO NOT play the haunting game at all and don't hide their true form. Usual encounters with these equal death unless something equal or greater interferes on one's behalf.