Piast/Biast/Bestia

The Piast is a monstrous creature from Irish myth. They are described as giant lake monsters, being part salmon and part serpent. They are also thought to be capable of breathing fire. It is believed Piast are one of the kinds of monsters banished by St. Patrick until judgment day.

Citations:

Bane, Theresa. Encyclopedia of Beasts and Monsters in Myth, Legend and Folklore. United States, McFarland, Incorporated, Publishers, 2016.