Gwrach y Rhibyn is a monstrous Welsh spirit in the shape of a hideously ugly woman.
Origin
Some speculation has been asserted that this apparition may have once been a water deity, or an aspect of the Welsh goddess Dôn. Gwrach y Rhibyn is also the wife of Afagddu, the despised son of Ceridwen and Tegid Foel, in some retelling of the Taliesin myth.
Etymology
A Welsh saying, to describe a woman without good looks, goes, "Y mae mor salw â Gwrach y Rhibyn" (she is as ugly as the Gwrach y Rhibyn)
Appearance
Gwrach y Rhibyn is said to have a harpy-like appearance: unkempt hair and wizened, withered arms with leathery wings, long black teeth and pale corpse-like features.
Behaviour
Gwrach y Rhibyn approaches the window of the person about to die by night and calls their name, or travels invisibly beside them and utters her cry when they approach a stream or crossroads, and is sometimes depicted as washing her hands there.
Most often the Gwrach y Rhibyn will wail and shriek "Fy ngŵr, fy ngŵr!" (My husband! My husband!) or "Fy mhlentyn, fy mhlentyn bach!" (My child! My little child!), though sometimes she will assume a male's voice and cry "Fy ngwraig! Fy ngwraig!" (My wife! My wife!).