Today’s yokai is a pretty frightening sight. Ohaguro-bettari is said to appear at twilight. She wears a beautiful kimono, sometimes a wedding dress, and often hides her face, turning away so that she appears to be a beautiful young woman. When a young man approaches close enough to see her, she turns, revealing her split-open face with a mouthful of blackened teeth — and no other features — and screams at them.
Blackened teeth were once a very fashionable thing, and you can do a quick image search to find old photos of people with blackened teeth from all over the world, and especially East Asia — not just Japan. It’s a pretty creepy fashion by itself, let alone if the person doesn’t have a face. So remember, stay away from beautiful women at night!
By the way, Pink Tentacle has an article about a Hyakki Yako scroll for sale on eBay (if you can afford it — $15,000!). This scroll — “The Night Parade of One Hundred Demons” — is a very famous illustrative source of yokai. Take a look!