This one is really creepy. 'The mirror fogged up, but I was alone in the bathroom. A handprint appeared on the glass.' It gives me chills just thinking about it. The idea that something is in the bathroom with you when you thought you were alone is a classic horror trope, and the handprint on the fogged - up mirror makes it even more terrifying.
Well, 'The doorbell rang at midnight. I opened the door to an empty porch, but wet footprints led into my house.' Midnight is often associated with the unknown and danger in horror stories. The empty porch but the wet footprints leading inside is a great source of unease. It makes you think that something invisible or very sneaky has entered your home.
I looked in the mirror. My reflection smiled and blinked without me doing it.
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.
I woke up to a noise. When I turned on the light, a shadow figure was standing at the foot of my bed.
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.