The thing about horror films is that the closer they are to actually being able to happen in real life, the scarier they are. If that's the case, then I propose the following potential plots as the scariest horror movies of all time. (All agents, feel free to contact me. Will sell for moderate financial sum and your first born child. Kidding. I don't want a kid.)
1. TomTom goes KillKill
She was just following directions.
At first you think your GPS is just messing up again, like always. You keep following it's directions, all the while muttering swear words under your breath. But still, you keep driving. TomTom directs you to a remote corner of town. You keep driving. TomTom tells you to go the opposite direction. You keep driving. Soon, the TomTom screen goes green and shows that you are now not even on a real road, you're just driving through grass. You keep driving, your car bumping along. But now you really are in a field. Lost and alone. And then TomTom goes KillKill and someone attacks you.
2. SnapChat Serial Killer
One snap from death...
You receive a terrifying SnapChat of your friend's bloody face. The killer/kidnapper continues to send you SnapChats of clues as to where you can find your friend. You try to take a screenshot so you can take the clue to the police, but the SnapChatter kills off a family member in warning. For every screenshot, one life will be lost. You wildly follow the clues. Worse yet, you can't trust anyone around you because by the very nature of SnapChat, this means that the kidnapper/killer is someone you know and who already had your number.
3. The Twin from Beyond
What would you write, if you'd never had the chance before?
A friend recently told me that leading scientific theory is that every left-handed person at one point had a twin who they killed in the womb. I literally cannot look at left handed people anymore without fear. Do they know they kill someone? In this horror film, a left handed person would be taken over by the right handed twin they killed in the womb. The right handed twin would take over their right hand and leave scribbled, fearful messages.