When Cúchulainn returned to Emain Macha after his first foray, his fury was so great the Ulstermen feared he would destroy them. Mugain led her maidens out, and they bared their breasts in front of him. Cúchulainn averted his eyes, and the Ulstermen were able to wrestle him into a barrel of cold water, which exploded from the heat of his body. They put him in a second barrel, and the water boiled; and finally a third barrel, which merely warmed up to a pleasant temperature.
Her affair with Áed, Conchobar's poet, led to the death of Lóegaire Búadach.