Yama-uba is a mountain witch or hag from Japanese culture.
The issue with Japanese creatures and myths, at least from western eyes, is that Yama-uba could be a witch, a hag, a ghost, a demon or somehow all the above at the same time! Certainly makes them fun.
What separates these creatures from western hags is that the Yama-uba has a second mouth on the top of her head. She uses this one to eat while her "regular" mouth can be used to hold conversations. Interestingly this does not make her unique in Japanese culture. The Futakuchi-onna also has a second mouth on the back of her head. Maybe in myth these started out as the same creature and then split or two local creatures that adopted the same traits.
The Yama-uba is described otherwise very much like the western Hag; old, large and potentially cannibalistic. Alternately she is also described as having a dark face with large white eyes.
This has lead to a couple of strange pop-culture trends in Japan. First is the Pokemon Jinx, that looks like the descriptions of Yama-uba. She is of course a psychic Pokemon.
|Ventisca the Yama-uba|
AC: 5 
Hit Dice: 10d8+10* (54 hp)
No. of Attacks: 2 claws + 1 bite
Damage: 1d8/1d8 + 1d6
Special: Charm, Dance, Shape Change, Spell use
No. Appearing: 1
Saves As: Witch 10
Treasure: 1d12 Gems (1d10x10 gps each)
Yama-uba is large creature related to the common hags and the night hag. She has two forms that are her most often used. The first, and the one that many claim is her true form, is that of a grossly bloated hag. Her hair is black and wiry and her skin is molted and yellow from disease. Open sores cover her skin and her breath is foul. Due to her size her movement is slowed.
Her second form, Yamanba, is more appealing. Her skin is dark, almost blue or violet and her hair varies from light blonde to platinum. In this form she move twice as fast. There must be some reason why she can't remain in this form.
In both form the Yama-uba favors red dresses.
The Yama-uba is a cannibalistic monster that prefers to eat small children, but like many hags she has been known to care for children that evil parents have left to die.
The Yama-uba can cast any charm-like witch spell as a 10th level witch. She will typically augment this with dance which in her Yamanba form will provide a -2 penalty to any save vs charm.
Yama-uba, despite their appearance and diet, are often sought out for magical advice. If the Yama-uba so decides she can grant as many boons as she likes. Typically this takes the shape of either knoweldge or a +1 to hit, damage and saves for 24 hours. She can also just decide to eat anyone that walks into her land.