Blodeuwedd was created by Gwydion from oak broom and gorse as a wife for his son/nephew Lleu Llaw Gyffes. Blodeuwedd has an affair with Gronw Pebr, the lord of Penllyn, and the two conspire to murder Lleu. She tricks Lleu into revealing how he may be killed, since he can not be killed during the day or night, nor indoors or outdoors, neither riding nor walking, not clothed and not naked, nor by any weapon lawfully made. He reveals to her that he can only be killed at dusk, wrapped in a net with one foot on a cauldron and one on a goat and with a spear forged for a year during the hours when everyone is at mass.
With this information she arranges his death. Struck by the spear thrown by Gronw's hand, Lleu transforms
into an eagle and flies away. As punishment for her part in the incident Gwydion corners Blodeuwedd and turns
her into an owl, the creature hated by all other birds.