Question for Christians on Demonology

[Lism]

Today some Catholic guy on InstaGram was talking about how he uses the rosary to pretect him against a "generational demon" that killed his brother. Apparently his brother took his own life. Many atheists were angry in the comments about this sort of voodoo sounding attitude, but I am wondering what exactly Christians think is implied here.

Is a demon an actual magical being, not grounded in anything physical, that possesses you? Or is the demon more like a geist, a sort of essence of a malady, that expresses itself in the physical form of genes that cause suicidality?

In a similar case, when people say "pagan gods are demons", do they mean that demons have appeared on earth to convince people they are pagan gods? Or is the demon simply the sort of intellectual manifestation of that bad idea?

 

[BrimBurner]

Christianity is a massive religion with many divisions/denominations/beliefs, so I can't answer for everyone. But I will give my own perspective.
Demons are fallen angels, so that means they are much more powerful than us humans. Angels were created before humans, so they know everything about us.
But they are powerless compared to God, so they can't "possess and attack" us until the end times.
But we humans have a great weakness of free will and an urge to sin. Demons egg on those sinful desires and cause people to become their worst selves. I don't believe in a demon attack or a possession. If such a thing exists, prayer and a cross will defeat it easily.
But don't underestimate demons; they are much more dangerous if they are intelligent, powerful creatures doing everything they can to push us to sin and misery. Think about how miserable and mentally ill modern society is; so many people suffer from random depressive thoughts, intense suicidal thoughts, urges to drink or do substances and sexually degenerate desires. As Christianity is rejected more and more in this modern world, the more powerful these demons get.
These demons aren't some crazy fairy tale monsters you haven't encountered before, but you have encountered them, the thoughts in your head telling you to sin, the thoughts that make you feel hopeless and miserable. They do exist physically somewhere, banished suffering for eternity, and the only thing they can do is attack the fragile creations of God, wanting to drag down as many humans to them as possible.