The Gwyllion is a creature from the folklore of Wales.
Also called 'Old Woman of the Mountain'
They are ugly old women usually described as wearing ash colored clothing with an oblong four-pointed hat, and carrying a pot in one hand. They also are known by their disturbing laughter and their cries of "Wow up!" This is an English form of a Welsh cry of distress) ' Wwb!' or 'Ww-bwb! [Pronounced Wooboob].
They live in mountainous areas and love to mislead travellers or scare them.
Many times they will just bother the traveller or possibly frighten them sitting on either side of a mountain path and following him with their eyes. However, if a Gwyllion in disguise manage to enter your home, it is recommended to treat her right and she will leave by herself without doing harm. The Gwyllion is repelled by metal knives, and a flash of a knife is usually enough to send a Gwyllion away.
The gwyllion are typified by the Old Woman of the Mountain who haunts Lanhyddel Mountain in Monmouthshire.