Well, there's this one. 'My phone took a picture by itself at 3 am. The photo was of an empty corner, but I felt a presence.' The idea of a device acting on its own and the sense of a presence that can't be seen but is hinted at is very spooky. It makes you wonder what could be in that empty corner that the phone seems to be aware of.
One scary one is 'The old dormitory elevator always groaned. Today, it sang a lullaby.' The sudden change from an ordinary, if a bit concerning, sound to something so much more eerie makes it quite frightening.
I think 'I saw a figure in the hallway mirror. When I turned, no one was there.' is really scary. Mirrors are often used in horror to create a sense of the unknown and the idea that something might be lurking just out of sight.
One: 'I heard a strange scratching at my window all night. In the morning, I saw the marks were from the inside.'
Well, the one where 'I woke up in a coffin. As I screamed, I realized I was buried six feet under.' is quite terrifying. Just the thought of being trapped alive underground is a nightmare.
Another really scary one could be 'My phone rang at 3 am. The caller ID said it was me.' It plays on the idea of the self being something other or unknown, and calls at that time are always spooky.
One of the scariest collegehumor ghost stories is from a college's old science building. There were rumors of a ghost of a failed experiment. Students working late in the labs often heard strange bubbling sounds that couldn't be explained by any of the equipment. Some even claimed to see a figure covered in some sort of gooey substance wandering the halls.
Well, there's 'My daughter won't stop crying and screaming in the middle of the night. I visited her grave yesterday.' Also, 'I heard a noise from the basement. The power has been out for days so it couldn't be the furnace.'
I woke up to the sound of scratching at my window. When I opened my eyes, a shadowy figure was peering in.
The sudden and unexpected events. For example, a character thinking they are alone and then suddenly seeing a shadowy figure right behind them.
The sudden appearance of unknown entities. For example, a figure suddenly showing up in a supposedly empty room.
I think 'I heard a child crying in the basement. But I live alone.' is quite terrifying. The idea of a crying child in a place where no child should be, especially when you live alone, plays on our fears of the unknown and the supernatural. It makes you wonder what could be down there, and the thought that it's not a normal, explainable situation is very frightening.
I think 'The clock stopped at midnight. Then I heard footsteps.' is quite scary. It gives this feeling of something ominous starting right at a spooky time.