This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Futakuchi-onna (Japanese)
Futakuchi-onna is a type of yokai or Japanese monster. She is characterized by her two mouths, a normal one located on her face and a second one on the back of the head beneath the hair. There, the woman's skull splits apart, forming lips, teeth and a tongue, creating an entirely functional second mouth.
The origin of futakuchi-onna's second mouth is often linked to how little a woman eats. In many stories, the soon-to-be futakuchi-onna is a wife of a miser and rarely eats. To counteract this, a second mouth mysteriously appears on the back of the woman's head. The second mouth often mumbles spiteful and threatening things to the woman and demands food.