Slenderman was a boogeyman created by the YouTube world, and it actually became quite popular, spawning video games, books, comics, and even a few movies. Unfortunately, two 12-year-old girls decided to appease the mythical being by stabbing their friend to death in a sacrificial manner.
The Wicker Man
The Wicker Man is known as a remake starring Nicolas Cage, but the original tale was a bit more haunting. According to 10th-century documents, people sacrificed each other by placing them inside of wicker statues and lighting them on fire.