They "happened" when a creative writer, took up his pen and described a new kind of a monster, using the imagination to create a condition of fear, to lend excitement to a story.
Now if you want the one's in the "real world" you are safe, they have not happened, unless you are sucked into one of the sony play stations worlds of zombies, werwolves and vampires. Then you are going to get murdered.
Yer not serious are u?
They say eatin ain't cheatin... But they were wrong.....O.o