In the Amityville Horror, the scariest part was the presence of the demonic figure. Just the thought of seeing a pig - like, demonic entity in your own home is terrifying. The slime on the walls and cold spots were also very creepy, but the idea of an evil being in the house really takes the horror to another level.
The most terrifying part is often the unknown. In these stories, it could be not knowing what's making that strange noise in the haunted house or who the ghostly figure really is.
The feeling of being watched is really terrifying. In spooky stories, characters often sense that there's a presence observing them. It gives a sense of vulnerability. Take the story of the haunted asylum. The patients there were said to feel like there were eyes on them all the time, which added to the horror. Also, the idea of something being out of place, like a door opening by itself or objects moving on their own, is very scary. It goes against the normal order of things we're used to.
In some of the stories, the sudden appearance of the supernatural entities is the scariest part. Like in the haunted house story, when a ghostly figure just pops up in front of you out of nowhere. It gives you an instant shock.
The scariest parts often involve the strange noises Greg hears at night. It gives a sense of mystery and unease.
The unexpectedness. For example, in a story about a spooky mirror, you might think it's just a normal mirror at first. But then suddenly it shows a face that's not yours, and that sudden shock is a really scary part. It's the element of surprise that makes dumb scary stories effective.
For me, the scariest is the voices. In exorcism stories, the possessed often speak in strange voices that are not their own, sometimes multiple voices at once. These voices can be guttural, demonic-sounding, and they often say things that are disturbing or full of hatred.
The suddenness of the attack. For example, when you least expect it, a wasp just dives at you. It gives you no time to prepare.
The sense of isolation. When a person is alone and a strange person shows up, like the man in the motel. He was in a strange place all by himself, and the appearance of the stranger made him feel even more alone and vulnerable. There was no immediate help available, which is really terrifying.
The sudden appearance of something strange. In the story of the face at the window, the babysitter is just going about her job, and then suddenly there's this creepy face. There's no warning, and it's something that seems out of place and threatening, which is really terrifying.
In many pikachu scary stories, the sudden change in Pikachu's behavior is terrifying. It goes from being a lovable Pokémon to something aggressive and unpredictable. For instance, when it attacks without any provocation or starts to make inhuman noises. Another really scary aspect is when Pikachu seems to be under the control of some dark force, and it uses its electric powers in a way that is more harmful and destructive than normal.