One of my experiences on my mission involved "demon possession". We were called to an investigators home whose daughter was . . . crazy. I can't remember if it was a leader of the district who asked us to come or if we found this family on our own. We ended up talking to our mission president about it and received instructions on how to cast the devil out. I remember the girl convulsing while we were placing our hands on her head and the district guy holding onto her hair to keep her head in place. After the "casting out" we left and I don't think we ever went back.

A few weeks later something similar happened and the district president had us fast for 3 DAYS!!! to purify ourselves before we were to perform the exorcism. We showed up to the house where the demon child lived and the parents asked us politely to leave and never come back. I was exhausted from just drinking water and didn't really care at that point based on my last experience.

This brought up a discussion with my mission president that really baffled me. The converstation went something like this:
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[Me]
"I'm confused. I understand how the Holy Ghost influences me. The spirit runs through everything and HG uses that for a conduit. How does Satan do it? Does he use the same conduit? I thought it could only be used for pure purposes and shuts down when something wrong or sinful gets involved. Is there a dark spirit?"

[President]
"Think of a billboard with a bad picture on it. Satan knows that by putting that picture up there you'll have bad thoughts."

[Me]
"But Satan doesn't put the billboard up there, a real person decides to put that up there. How did Satan influence them?"

[President]
"It isn't safe to discuss how Satan really influences us, you should avoid thinking about this."

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Every time I tried to figure this out I would get a similar response. "Don't think about it, it's dangerous."

It's appalling that the "brethren" tolerate gross superstition like it's just a fluke.
BKP even said of false beliefs that ride piggyback on faith in the truth- "there's little harm in this".
"Demon possession" is a perfect example of superstitious social hysteria.
Carl Sagan devotes a chapter of Demon Haunted World to witch hunting, how there was a beaurocracy in place that profited from finding witches. The last known witches found in England were a mother and child who caused a rainstorm by taking off their socks. They were executed.
A TBM friend once confided in me that they had to do a depossession blessing on a sibling who had slept with an open mouth and the evil spirit entered her mouth.

OMG.
Sleep with your mouth taped shut.
Sleep with your hands tied to the bedpost.
Don't think or talk about Satan because you'll give away tactical intelligence he can use.

I've gotten advice to not talk about temple trips in advance because it gives Satan a chance to plan a sabotage.

Do demons watch you have sex?

Paranoia.

Meanwhile REAL threats loom.

My unstable TBM mother had me worrying about similar crap when I was little. Ouija boards invite the devil of course, so anytime I saw one I would immediately leave the building where it was contained, to avoid being possessed. Even when I was 19 and watched the Exorcist for the 1st time, I thought even watching that movie would invite the devil into my house. I was so worried about being possessed because my mother said any stray thought about the devil might invite him. Geez, I'm so glad that I'm away from f*ck#ng crazy people.

Don't look in a mirror and say "candyman" (or Satan or whatever) three times.

And nothing creates fear like the boogieman hiding unseen in the darkness ready to jump out and eat you up.

...with all the ways Satan can mess with our minds and hearts, how can Mormons know whether all they believe is the work of the devil?

If I tell a Mormon that yes, I did pray about it and got the confirmation that the church isn't true, they would say that spirit I felt was of the devil.

But what I'd reply is a set up. I'd say "That's silly. Satan can't influence you with good feelings." They would promptly assure me that yes, he can and I'd jump on that. I'd ask them how they can be sure of their testimony then, since all they have are feelings and all evidence and history and science are against them.

"And you just said Satan can lie to you with your feelings... Good luck with that."

I spend a lot of time thinking of what I'd say in a given situation, which is probably a waste since most Mos won't talk to me about Mormonism. Oh well, at least I'm exercising or getting housework done while I'm thinking. LOL.

It isn't safe to discuss how Satan influences us? What could be more important in the fight against evil?

It just goes to show, and I've said it before, Mormons are more afraid of Satan that they trust God. In fact, I'd venture to say that many mormons believe more fully in the Devil than they believe in God.

My dad told us when we were getting ready to go to the temple for the first time that my wife and I should write down our plans instead of discussing them out loud. Apparently the devil can hear you and thwart your plans. I should have asked why such a clever being couldn't read...

My grandmother claims that my mom cast a demon out of her one time using some sort of NewAge stuff that she gets mixed up in with her weird study groups (the Brethren approve but don't publicly endorse, doncha know...).

But that is the thing about mormonism- people are raised to be superstitious and to believe every thing that comes down the road, and to cower in fear until the Priesthood holder comes to the rescue. That and that they are trained to believe everything that a faithful member tells them, and to avoid outside thinking.

And look at the temple presentation- Lucifer has all the power.
God can't even tell whether Man is on the Earth, whether it is good to be alone, needs PJ&J to cast Lucifer from Adam and Eve's midst. And Lucifer tells the Patrons to put on an apron, but none of the leaders, officiators, or any of the characters in the drama.

Not only that, but only Lucifer ever speaks directly to the audience. God and Jehovah never do. They never even teach, but give all power and authority to Priesthood holders.

The subconscious message here is that we are all subject to satans power, and only the Priesthood of the Mormon Church has the power to save us. And not only that, but the God that we will become is an extension of ourselves and all of our weaknesses. Thus, not really very powerful.

So is it any wonder that mormons are so fearful?

well spoken.
I've called it "My personal relationship with satan" complex.
That is, I believed satan was literally watching every move and taking advantage of every twitch that might give away a sinful thought that he could incubate.

The Boogeyman lived in the closet, but could be stopped by closing the door.

The crocks could only get you if your feet were dangling out of the covers.

BTW - the "covers" were 100% monster-proof.

Ah! Life was simpler then.

I just don't believe in that cr*p and never have.