The main attack of the noppera-bo ("featureless" in Japanese) is to scare the pants off people by randomly showing up in places (often ladies' rooms) and then revealing their smooth featureless faces, although they can also appear with just a mouth or teeth. Noppera-bo is also one of the most international of yokai; many sightings have been reported in Hawaii, where it is called a mujina.
The trickster tanuki in Studio Ghibli's Pon Pokomovie use the image of noppera-bos to try to scare away some construction workers threatening their home. Faceless aliens in one of the Hetalia movies are called "nopperas." The image of a face with only a mouth also shows up in a lot of shows, a well-known example being that of the Gate (or Truth) character in Fullmetal Alchemist.
