The scariest elements are often related to the atmosphere. Dark, damp, and cold places tend to create a sense of dread. For example, in an abandoned underground bunker, the lack of light and the stale air can make you feel claustrophobic and scared. The idea of the supernatural is also very scary. If there are rumors of ghosts or other unearthly beings in the place being explored, it heightens the fear. Also, finding things that are out of place, like a child's doll in an old factory, can be really creepy. It makes you wonder how it got there and what it might mean.
The isolation is a really scary element. When you're in an abandoned place like an old building or a tunnel, you're cut off from the normal world. There's no one to help if something goes wrong. Another is the unknown history. You don't know what happened there in the past, whether it was a place of death or some kind of cruel experiment. The strange noises also add to the horror. They can come from anywhere, and your mind starts to imagine all kinds of terrifying things that could be making those noises.
I think the sudden and unexplained events are the scariest. Like when flashlights start flickering for no reason, or when you hear strange noises that seem to come from nowhere. In some stories, doors close on their own or objects move. These things defy logic and make you feel like there are supernatural forces at play in those abandoned urban areas.
The idea of the supernatural is really terrifying. For example, in the 'Crying Baby Bridge' legend, the thought of a ghostly baby crying from beyond the grave is spooky. Also, the lack of control. When faced with something like the 'Slit - Mouthed Woman' in the story, the victims have no real way to defend themselves or escape easily.
The sense of the unknown. In many Japanese urban legend horror stories, there are no clear explanations for why these things happen. For the Aka Manto in the toilet, there's no backstory as to why he is there or what his true motives are. This lack of knowledge makes the stories even scarier as our minds start to fill in the blanks with the most terrifying possibilities.
The unknown. In the city, there could be all sorts of things lurking in the shadows. Maybe it's an abandoned building with a dark past or a hidden underground space. You don't know what you might stumble upon. It could be a homeless person with malicious intent or some kind of supernatural presence. Like in one story, a camper found a hidden basement in an old building he was camping near, and when he went down, he felt an overwhelming sense of dread for no obvious reason.
The scariest element could be the sense of the unknown. For example, in many stories, there are strange noises or happenings that the characters can't explain. It's that not - knowing what is causing the fear that really gets to you.
The isolation in many of the stories is really scary. Like when a character is alone in an old, abandoned building, cut off from the outside world, and they start to feel like they're being watched by something malevolent. There's also the fear of the supernatural, such as ghosts or demons that defy the laws of nature. This makes the characters, and the readers, feel powerless against them.
The unknown is the scariest element. When a stranger appears in a horror story, we don't know their motives or what they are capable of. For example, in the story where a stranger gets into a car, we don't know if they are a ghost or some kind of malevolent spirit. Their sudden and unexplained actions are terrifying.
The idea that slime could be alive or sentient is terrifying. For example, when the slime in the laboratory became aware and started to attack people. It goes against our normal understanding of non - living substances. Also, the fact that it can engulf things, trapping people or objects within it. It gives a feeling of helplessness as there's no easy way to escape from a mass of slime.
The scariest element is often the presence of vengeful spirits. These spirits are usually the result of some injustice or tragic death in their past lives. For example, a woman who was wronged and killed might come back as a ghost to seek revenge on those who wronged her.
The distortion of the normally cute and friendly ponies is quite scary. When they become menacing or possessed - like, it's a big contrast to what we expect from MLP. For example, seeing Pinkie Pie with a blank stare and a menacing grin instead of her usual happy face.