The Black Cauldron (1985)
- Quite a number of significant characters were omitted from the film, including Coll, an assistant to Dallben, an evil queen/witch named Achren, a war hero named Gwydion, and an evil lord Arawn who was actually the master to the Horned King.
- Also missing is Ellidyr, a prince who sacrifices himself to the Cauldron; Gwystyl, a Fair Folk who has a way post near Annuvin; Adaon, Son of Taliesin; Medwyn, an enchanter who helps the companions; Morgant, a king who tries to use the Cauldron for himself; Smoit, a king who helps Gwydion find the Cauldron; and Kaw, a crow who can talk.
- In the books, Princess Eilonwy is described as having red-gold hair and bright blue eyes, but in the film, she has long blond hair and light blue eyes.
- Dallben had a beard in the books, perhaps having an appearance closer to Gandalf, in "The Lord of the Rings".
- Creeper, who served as the henchman to The Horned King, is an added character in the film, not found in the books.
- Fflewddur Fflam is described as having more yellowish hair in the books, as well as being lankier and much younger than what he appeared as in the film.
- In the first novel, "The Book of Three", Taran does, indeed, find Dyrnwyn (the magical sword), but is injured when he attempts to clear it from its scabbard. Dallben later tells him that had he drawn it completely, it would have likely killed him. (He is able to wield it in the fifth novel, "The High King", since by that point he is able to draw it "for noble worth").
- The Horned King did not try to get his hands on the Black Cauldron. Unlike the film where the Cauldron is hidden and being sought by the Horned King, in the books the Horned King was the servant to the evil lord, Arawn, who already owned the Cauldron to release the Cauldron-Born. In the beginning of the second book, "The Black Cauldron", the good characters planned to steal it from Arawn, only to find it had already been stolen (by the Witches of Morva).
- In the first book, Prince Gwydion defeats the Horned King by shouting his true name aloud. In the film, the Horned King dies by being swallowed up by the Cauldron.
- In the film, Doli is clearly able to disappear/become invisible. In the first book, "The Book of Three", Doli's main wish is to be able to have the power to become invisible.
- In the film, Taran meets Eilonwy in the dungeon of the Horned King's castle. In the first book, "The Book of Three", Taran was trapped in the evil witch, Achren's castle, and was then rescued by Eilonwy.
- In the film, Taran and Eilonwy meet Fflewddur Fflam in the dungeon. In "The Book of Three", however, Taran and the war hero, Gwydion are separated in different dungeons. Taran sends Eilonwy to rescue his war hero friend, but mistakenly takes Fflewddur Fflam for Gwydion.
- At the end of the film, The Horned King's castle collapses. In the middle of the first book, Achren's castle collapses.
- There were inconsistencies in character motivations. Doli is presented as a bit of an oaf in the film, when in the books he is an ill-tempered but talented craftsman. Eilonwy is much more hot-tempered, stubborn, sarcastic, and resolute in the novels than in the film. The Witches of Morva, in the second novel, are more care-free about the Black Cauldron, opting to trade it to Taran for Adaon's Brooch. When the Witches (who really aren't all that afraid of Arawn or the Horned King) meet the protagonists, they are much more motherly and kind and much less sinister and cruel.
- In the film, Gurgi puts his body into the cauldron to destroy its powers. In the second book, however, it was a character named Ellidyr. Ellidyr goes into the Cauldron and dies. (In the film, Gurgi died, but was brought back to life by the Witches of Morva.) The Cauldron is also destroyed when Ellidyr jumps into it, but he is not restored to life. The Cauldron is destroyed, but Arawn's Cauldron-Born warriors still serve him.
- In the film, Hen Wen is a piglet. In the books, she is a full grown white sow.
- In "The Book of Three", Hen-Wen runs from Caer Dallben because she is frightened by the nearby presence of the Horned King. Taran is hooked into his adventure when he chases after her to return her to Caer Dallben. Dallben wants to keep her home so she can read a prophecy that might help them fight the Horned King. In the film, however, Dallben is sending Hen-Wen away with Taran to keep the Horned King from getting her.
- In the film, Hen-Wen uses her oracular abilities by gazing into a dish of water. In the books, Dallben has a set of ash-sticks with symbols carved on them. Hen-Wen, then, points to the symbols with her snout to dictate the prophecy.
- In the film, Eilonwy's bauble is depicted as a semi-sentient object which floats through the air under its own power. In the books, it is described more like an orb of gold which must be carried.
- In the film, Eilonwy tells Taran that the Horned King kidnapped her so that her bauble would give him information about the Black Cauldron. In the books, Eilonwy lives, more or less reluctantly, with her "Aunt" Achren, who is keeping Taran prisoner.
- In the film, Taran and the others are pulled into the Fair Folk realm by mistake. In the books, the lake is made to pull people in on purpose, as it is felt that if they reach the lake, they are already "too close" to Fair Folk territory to leave.
- In the film, Doli is depicted as a fairy. In the books, he is depicted as a dwarf.