Fflewddur has a magic harp that will break a string or two every time Fflewddur tells a lie or colors in the facts, which he does somewhat frequently (i.e. exaggerating his own courage or musical talent). His catchphrase is "Great Belin!", the witch Orwen has a romantic interest in him while Orgoch wants to turn him into a frog and eat him. Fflewddur, however, has his moments of bravery such as when he stands up to the witches so that they will revive Gurgi. Though not specified in the film, in the books Fflewddur is a king of a rather small kingdom and generally prefers to travel as a bard across Prydain.
Fflewddur first appears in the film in the dungeons of the Horned King being menaced by a pair of chained attack dogs. He is freed by Eilonwy and Taran and joins their escape from the Horned King's castle. Afterward, Fflam is attacked by Gurgi, but the latter turns away after he realizes Fflam is a friend of Taran, who he likes. The four of them proceed to Morva, where they encounter three witches, one of whom is in love with him. After the new team realizes they don't know what to do with the Black Cauldron, he is ultimately recaptured by the Horned King. But Gurgi sneaks into the castle and rescues him along with Taran and Eilonwy. After which Gurgi sacrifices himself to the Cauldron so Fflewddur and the others could escape the castle alive.
Fflewddur convinces the three witches to accept the proposed deal of Taran returning the Black Cauldron to them in exchange for their bringing Gurgi back to life. After they do so, Fflewddur and the other heroes happily leave, taking Taran home to Caer Dallben.