Most scary movies suck, they just rely on blood and gore. However, one movie has succeeded in giving me nightmares. Fire in the Sky. Its based on a true story of alien abduction. I was around 12-13 when it came out, saw it once and never again . If I watched it now, I'd probably be fine, but back then that was terrifying. I don't know, I just guess aliens are scarier than monsters because they could be real.