Here's another: 'The old house was silent. Then I heard the doorknob turn slowly.' This creates a sense of dread as the unexpected sound in a silent place is quite scary. The slow turning of the doorknob implies that something or someone is about to enter without permission.
A third one is 'I was alone in the elevator. It stopped between floors, and a cold hand touched my shoulder.' The idea of being trapped in an elevator is already a bit nerve - wracking, and then the addition of the cold hand makes it a truly horrifying scenario.
One could be 'I woke up in the middle of the night. There was a figure at the foot of my bed.'
One good line could be 'The darkness seemed to breathe, a living entity that wrapped itself around me.' It creates a sense of the environment being alive and menacing.
One: 'I woke up to a noise. It was my own scream from the future.'
One 'two minute horror story' could be about a girl who wakes up in a strange room. The walls are closing in and she hears a faint whispering. As the walls get closer, she realizes the whispering is saying her name, but she has no idea how she got there. It ends with the walls about to crush her.
The old house stood at the end of the lane, its broken windows like empty eye sockets staring into the void. This opening line creates an image of a desolate and potentially haunted place, drawing the reader in.
One great line is 'It was a dark and stormy night, and the howling wind seemed to carry the whispers of the dead.' It sets a spooky mood right away.
They are effective because they are concise. For example, 'She heard a whisper. It came from inside the wall.' It gives just enough information to let your imagination run wild.
One could be: 'I found a key. It was old and rusty. I put it in a lock. A secret door opened. A world of magic awaited.'
One could be 'The game loaded, a familiar world at first. Then the glitched faces of loved ones stared back, their screams silent.'
I always thought my dog was protecting me. Last night, I saw it standing over my bed, its eyes glowing red.
Well, consider 'She found the letter on a sunny Tuesday morning, but it felt like a cold winter day.' This first line is interesting because it juxtaposes the pleasant day with the cold feeling that the letter brings. It makes the reader curious about what's in the letter and why it has such an effect.