[W efnys, hostile enemy, unpeaceful).
Malevolent and enigmatic son of Euroswydd and Penarddun in the second branch of the Mabinogi, brother of the benevolent Nisien [W, peaceful], and half-brother of Bendigeidfran, Branwen, and Manawydan. An easily insulted troublemaker, Efnisien causes much strife between Wales and Ireland. He disfigures the Irish horses, bringing war with the Irish, because he has not been asked for his consent when Bendigeidfran promises Branwen in marriage to the Irish king Matholwch. When it appears that Irish attempts to find reconciliation with the Welsh will succeed, he snatches Gwern, Branwen and Matholwch's son, and throws him into a fire, renewing hostilities. But Efnisien can be heroic and self-sacrificing. He saves the life of Bendigeidfran and the Welsh invaders when he slaughters 200 Irishmen. And he sacrifices his life when he stretches out in the cauldron of rebirth; as it is intended only to resuscitate the dead and Efnisien is still living, his martyrdom bursts it. Some commentators rationalize Efnisien's action by portraying him as a guardian of Welsh sovereignty, as embodied in Branwen. Others see him as an ill-tempered agitator like the Irish Briccriu; see FLED BRICRENN [Briccriu's Feast].