The Morrigan

“it is at the guarding of thy death that I am; and I shall be …when thou art in combat against a man of equal strength, equally rich in victories, thine equal in feats, equally fierce, equally untiring, equally noble, equally brave, equally great with thee, I will be an eel, and I will draw a noose about thy feet in the ford, so that it will be a great unequal war for thee.”
The Ulster Cycle, The Cattle-Raid of Regamna