During the Battle of Cath Godeau, Gwydion turned trees into warriors, thus winning the war begun by his brother, Amaethon.
Gwydion raised his nephew, who was born a blob. The blob was placed in a chest by Gwydion. Arianrhod, the blob's mother, created three geases: only she could give him a name; only she could give him weapons; he would have no human wife. Arianrhod denied him the three aspects of masculinity. Gwydion raised him anyway, even without a name. Later Arianrhod saw him killing a wren with a single stone. She said that he was a bright lion with a sure hand and he took the name Llew Llaw Gyffes ("bright lion with a sure hand"). Gwydion then tricked her into arming him. Llew created his own woman out of flowers, Blodeuwedd. After Llew Llaw Gyffes was killed by Blodeuwedd, Gwydion resurrected Llew and turned her into an owl.