Afanc is a lake-monster from Welsh folklore that differs highly in appearance depending on the story, being anything from dwarf, beaver, crocodile or anything in-between, it is sometimes said to be a demon but it is most usually depicted as a large frog with claws on all limbs and seems more akin to a fey than a traditional demon.
Regardless of form the Afanc was said to prey upon any foolish enough to fall into or swim in its lake.
The most common story that surrounds the Afanc is that a town was plagued with its carnivourous activities so much that they resolved if they could not kill it they would take it to another lake away from them.
They employed the Afanc's one weakness, a beautiful woman, who lured the Afanc to sleep upon her lap.
The villagers then captured the Afanc with magical chains and used two oxen to drag the creature across to the next lake.
Some later legends say that once the creature was dragged out of the lake it became powerless and was killed by Peredus, or King Arthur depending on which tale you read.
Close to Llyn Barfog in Snowdonia, is a hoof-print petresomatoglyph etched deep into the rock "Carn March Arthur", or the "Stone of Arthur's Horse", which was supposedly made by King Arthur's mount, Liamrai, when it was hauling the Afanc from the lake.
Lolo Morganwg put forth a tale in which the creature's thrashings caused massive flooding which ultimately drowned all inhabitants of Britain except for two people, Dwyfan and Dwyfach, from whom the later inhabitants of Prydain descended.