* AnticlimaxBoss: [[spoiler: Arawn]], despite his build up, he just [[spoiler: turns into a snake which is promptly killed by Taran in book five]], [[Disney/TheBlackCauldron The Horned King who shares many characteristics with his personality]] also suffered from this.
* CargoShip: Fflewddur and his harp.
* DesignatedHero: Taran's foolhardiness and [[GloryHound obsession with his own glory]] in the early books leads many readers to wonder why we are to cheer him on. He gets better.
* EvilIsCool: The Horned King, [[EnsembleDarkHorse he was notable enough to be promoted to Big Bad of the Disney adaptation of the Black Cauldron]]
* EnsembleDarkHorse: Despite appearing in only a few scenes, the Horned King was notable enough to be promoted into BigBad in the adaptation of the second book
* FridgeLogic: [[spoiler: Okay. Dyrnwyn can kill the Cauldron-Born. ''Why'' did Gwydion not twig onto this while he had it in his possession?]]
** [[spoiler: Taran tried using it on the Horned King. The sword was too dangerous to use at the time.]]
** [[spoiler: Also, how often do you try to stab things that you know can't be harmed? Bear in mind that they hadn't read the full version of Dyrnwyn's runes yet.]]
** [[spoiler: Most importantly, the Cauldron-Born haven't been around since the second book since Arawn has been holding them in reserve now that he has a limited supply of them. The fact that they get weaker and slower the longer/further they are from Annuvin also makes them far more effective as guards than an assault force.]]
*** [[spoiler: And note that when Arawn is ready to use them, the first thing he does is steal the blade. And after using them, he immediately has them head for home.]]
* JerkassWoobie: Ellidyr. He spends pretty much the entire book being a jerk to everyone, but especially heaps scorn on Taran, going so far as to drag him bodily across Caer Dalben and take it for granted that Dalben would punish Taran for "impertinently" backtalking a prince. This reaches new levels around the climax, when [[spoiler:Ellidyr uses the heroes' desperation to bring the Black Cauldron to Caer Dalben as leverage to force Taran into agreeing to basically act as his servant and pretend that ''Ellidyr'' was the one who found the Cauldron (which is doubly cruel considering that Taran only got the Cauldron himself by giving up a brooch that his dead friend bequeathed to him). When they all agree to these terms, Ellidyr goes on to lose his mind and try to kill them anyway, somehow convinced that they were going to double-cross him.]] However over the course of the story, it's revealed that he's such a jerk because his family squandered their title of nobility and fortune, leaving him with virtually nothing but his title as a prince and his ill-tempered horse. [[spoiler:He also ends up severely beaten and taken prisoner while trying to bring the Cauldron back to Caer Dalben, and is horribly broken when he is unable to even free himself to save the group from death. He ends up [[HeroicSacrifice throwing himself into the Cauldron at the cost of his own life]] because that's the ''only'' thing he can do to help the others, and does so after swearing "on what little honor [he] has left" that he only wanted the Cauldron destroyed, and never intended to use it himself.]]
** To make it even more of a TearJerker, said ill-tempered horse [[spoiler: deliberately runs off a cliff in anguish at Ellidyr's death]].
* MagnificentBastard: Arawn.
* NightmareFuel: [[spoiler: Reading the final book, it seems that at least part of why actual displays of full-force magic are so rare in the series is that Prydain-style spellcasting results in this when fully unleashed.]]
** In ''Taran Wanderer'', Morda transforming the protagonists into animals is plenty creepy. Doli, who was turned into a frog, seems to constantly be ill, spasming at one point, and nearly dies from lack of water. When the rest are caught by Morda, he creepily ties them all up before enchanting them one by one, gleefully musing to Taran about how he wants to pick a form for him that's particularly humiliating and easy to enslave. And when Taran manages to free himself and fight back? [[spoiler:Morda used his magic to make himself unkillable.]] Even more scary, [[spoiler:Taran only found Morda's SoulJar completely by chance. If he didn't have it with him, not only would it have been impossible to kill Morda, but there would have been ''nothing'' to protect Taran from the ensuing attempted transformation spell after stabbing the guy didn't work.]]
* [[PlayerPunch Reader Punch]]: [[spoiler:Coll]]'s death.
* TearJerker: A half dozen in the last book, easily. [[spoiler: A very brief list - Coll's death far from home in a barren wasteland, Prince Rhun's death, Fflewdur Fflam destroys his beloved harp and has to leave Prydain forever, Doli and the Fair Folk leave the surface world, Gurgi has to go back to the Summer Country with the Sons of Don...]]