Cymidei Cymeinfoll

In the Second Branch of the Mabinogi Cymidei Cymeinfoll is presented as an Irish giantess who, with her husband Llasar Llaes Gyfnewid, lived under a lake in Ireland. They are brought into the court of Matholwch as guests at the wedding of Branwen; Matholwch later orders an iron building heated from the outside in which most of their household dies, but Cymidei and Llasar escape to Wales with the Cauldron of Regeneration and present it to Bendigeidfran as a peace offering.

Medieval sources provide only limited physical description. Cymidei is called a giantess (an Irish giantess in modern summaries) and is said to be smaller than her husband Llasar. Beyond size, the tale emphasizes her prodigious fertility — she gives birth to a fully formed armed warrior at regular intervals — and her dwelling under a lake; no detailed features, dress, or color imagery are recorded in the supplied sources.

The principal supernatural ability recorded in the tale is that Cymidei "gave birth to one fully formed and armed warrior every six weeks." Together with her husband she is custodian of the Cauldron of Regeneration: dead warriors are thrown into the cauldron and come back to life mute. In the narrative these powers make them strategically valuable and dangerous to human rulers, and they are central to plot events involving hospitality, attempted murder, escape, and the transfer of the cauldron to Bendigeidfran.