Walys sided with Rhaenyra Targaryen during the Dance of the Dragons and served as an important commander. He allied with House Brune, House Crabb, and House Celtigar to take Rook's Rest back from the greens after the Battle of Rook's Rest. The force took the green garrison by surprise and the castle was retaken successfully.
Lord Walys grew arrogant after his victory and decided to kill the dragon of King Aegon II Targaryen, Sunfyre, who had been wounded in battle previously. Walys led his best and bravest men out to slay the dragon, but they would be beaten with no survivors. The charred corpse of Lord Walys was recovered after the battle and his brother and heir, Lord Manfryd Mooton, eventually sided with the greens.