One story could be about an old, abandoned house. A family moved in despite the warnings. On the first floor, they would hear strange scratching noises at night. As they explored, they found a hidden basement door. In the basement, there was a dark figure that seemed to disappear when they turned on the light. Another story is of a hotel. A traveler checked into a room on the second floor. At night, he saw a woman in an old - fashioned dress in the hallway mirror. But when he turned around, no one was there. Every time he looked in the mirror, she got closer until he ran out of the hotel in fear.
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.
In two - story horror stories, the use of stairs can be a very frightening element. Stairs are often narrow and can be a bottleneck. If something is chasing you, the stairs can slow you down. Also, the upper or lower levels can have different atmospheres. The first floor might seem normal, but as you go up to the second floor, there could be a completely different and more menacing environment. Dark corners and hidden rooms on either floor add to the scariness as well. For instance, a hidden room on the second floor where strange noises come from can be terrifying.
They are concise. For example, 'The phone rang in the dead of night. It was my voice on the other end asking for help.' In just two sentences, it creates a sense of dread. They often rely on the unexpected. Like 'I found a door in my basement that wasn't there before. When I opened it, a cold hand grabbed mine.' It takes a normal situation and twists it into something terrifying.
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.
Here's another: 'The old doll in the attic blinked. I ran out and never went back.' This creates a sense of unease with the simple and unexpected actions. The blinking of the doll, which is an inanimate object, is very creepy.