
Rokurokubi: A female monster with an extremely flexible neck. By day they are indistinguishable from normal women, but after nightfall rokurokubi stretch their necks out to any length in search of prey. According to one theory, they are seeking out men in order to suck the life energy out of them.
You may recognize her from some anime series, like the Rurouni Kenshin episode where they went to the carnival.