The Gwyllion are female fairies of frightful characteristics, who haunt lonely roads in the Welsh mountains, and lead night-wanderers astray.

There was Evan Thomas, who, travelling by night over Bedwellty Mountain, towards the valley of Ebwy Fawr, where his house and estate were, saw the Gwyllion on each side of him, some of them dancing around him in fantastic fashion.
He also heard the sound of a bugle-horn winding in the air, and there seemed to be invisible hunters riding by.
He then began to be afraid, but recollected his having heard that any person seeing Gwyllion may drive them away by drawing out a knife.
So he drew out his knife, and the fairies vanished directly.