There are people born with an inherent gift to get information from the spirit world. The last one ודורש אל המתים ("one who seeks the dead") is common in the religious world. They think they are actually in communication with some spirit of some saint, but the spirit of the saint is in Heaven, and all these people talk to are demons that are super smart and know all there is to know about that tzadik (saint) and about the future.
[These all get the death penalty. I forget which one. (There are four types.) You should look up the Mishna in Tracate Kritut to find out which one applies.] The whole subject actually comes up in שמות Exodus 22:18 with the verse מכשפה לא תחיה and also in ישעיהו Isaiah 8:19
Everyone knows the story of Saul and Samuel. But few know the the reason he died was because of the event of not wiping out Amalek and also for seeking a familiar spirit as brought in Chronicles I 10:13-14 even though the last sin was not mentioned as the cause of his downfall in the book of Samuel.
One story brought in the Gemara was about one fellow who went to sleep in a graveyard and heard the spirits talking to each other and he found out what crops to plant that year. The spirits always give useful information but in the end they extract payment of one's life and family in this world and then in Hell.
The religious world presents a picture that looks similar to Torah in a few select rituals. It sounds like Torah in some ways. But instead of directing their service towards God it is directed towards idolatry.
People want to hear good stuff and how they are OK and if they join the club everything will be good for them. Secular Jews are largely at fault for this because they accept the frum (religious) narrative and all te money for yeshivas comes from secular Jews. If not for the monetary support and the compliant acquiescence of Reform and Conservative Jews the whole rotten structure of religious world would collapse.
There are demons that get into the head. This is the main problem.But there are many other types.
And the spirits have information that is not available to us. In the religious world every indication that someone has extra knowledge of the future or miracles it is assume they get it from the Bright Side. This assumption is usually false. Most of what are called "tzadikim" are people in connection with the dark spirit world and thus get amazing powers and knowledge.