The intended result came to pass—Pryderi invaded the land to recover his swine, Māth went to meet him in arms, and Gilvaethwy seized his opportunity and made Goewin his wife, although she was unwilling.
The war was decided by a single combat between Gwydion and Pryderi. “And by force of strength and fierceness, and by the magic and charms of Gwydion, Pryderi was slain. And at Maen Tyriawc, above Melenryd, was he buried, and there is his grave.”
When Māth came back he found what Gilvaethwy had done, and he took Goewin to be his queen, but Gwydion and Gilvaethwy went into outlawry, and dwelt on the borders of the land. At last they came and submitted themselves for punishment to Māth. “Ye cannot compensate me my shame, setting aside the death of Pryderi,” he said, “but since ye come hither to be at my will, I shall begin your punishment forthwith.” So he turned them both into deer, and bade them come hither again in a twelvemonth.
They came at the appointed time, bringing with them a young fawn. And the fawn was brought into human shape and baptized, and Gwydion and Gilvaethwy were changed into two wild swine. At the next year’s end they came back with a young one who was treated as the fawn before him, and the brothers were made into wolves. Another year passed; they came back again with a young wolf as before, and this time their penance was deemed complete, and their human nature was restored to them, and Māth gave orders to have them washed and anointed, and nobly clad as was befitting.
The question then arose of appointing another virgin foot-holder, and Gwydion suggests his sister, Arianrod. She attends for the purpose, and Māth asks her if she is a virgin. “I know not, lord, other than that I am,” she says. But she failed in a magical test imposed by Māth, and gave birth to two sons. One of these was named Dylan, “Son of the Wave,” evidently a Cymric sea-deity. So soon as he was baptized “he plunged into the sea and swam as well as the best fish that was therein.... Beneath him no wave ever broke.” A wild sea-poetry hangs about his name in Welsh legend. On his death, which took place, it is said, at the hand of his uncle Govannon, all the waves of Britain and Ireland wept for him. The roar of the incoming tide at the mouth of the river Conway is still called the “death-groan of Dylan.”