Afanc

An Afanc is a creature conjured using magic of the elements of earth and water.

Properties
It can only be defeated with magic, specifically the use of the oppositional base elements of fire and air. The Afanc is said to be a beast born of clay and conjured only by the most powerful sorcerers. In fact, Nimueh shaped a piece of clay into the figure of a small animal while chanting a spell ("Ic acennan eowic ac ic hredde eowic").

History
The sorceress Nimueh created an Afanc, magically transporting it inside an egg to the water supply of Camelot, where it hatched and caused a plague. Eventually, Arthur's manservant, Merlin, and the court-physician Gaius discovered the Afanc. With the help of Arthur Pendragon and Morgana, Merlin was able to destroy the creature using his own elemental magic (The Mark of Nimueh).