"The ancient prophecy: that a girl of ancient name shall become queen, that she shall choose a king, and that together they shall rule our world, and that their son shall rule the galaxy."
Blessed with Suck: The Cyclopes traded with the Beast: one of their eyes (which is why they only have one now) for the ability to see into the future. The Beast did give them the ability to see into the future - but they can only see the moment of their own deaths.
Casanova: Kegan (Liam Neeson), who has a wife or lover in numerous towns (or so it is rumored). Two wives are known of for sure, and while he never falls prey to Oops I Forgot I Was Married, he does have to do some quick thinking and fancy maneuvering to keep them from finding out about each other.
Convection Schmonvection: Played with. In the scene when Colwyn retrieves the Glaive from the lava pit, he clearly acts as if there is a great deal of heat rising from the pool, yet is still able to reach in and retrieve the weapon without burning himself or catching fire. However, this is justified by the fact he is the prophesied hero who would carry the Glaive, so its magic is implied to protect him from all effects of the lava. So, A Wizard Did It.
Did Not Do the Research: A glaive is actually a type of single-bladed polearm (and also an obscure name for a sword) not a five-bladed shuriken-discus. Though this may actually be a case of They Just Didn't Care motivated by Rule Of Cool, by combining an awesome weapon with the equally cool name of another. Considering the Glaive was "just an old symbol" and Krull was a place of mythical archetypes and cliches, there's nothing to say the name couldn't be attached to something different there anyway.
Disproportionate Retribution: Ynyr leaves the Widow to go off on his mad adventures, not knowing he had left Someone to Remember Him By. Furious and hurt, she kills their child after it is born. It is to the credit of Francesca Annis and Freddie Jones that the scene revealing this Moral Event Horizon, for which she was consigned to the web, is played with immense sympathy and tragedy thanks to the genuinely pity-inducing punishment she received and her clear regret for her crime.
Genius Loci: While not strictly alive or even sentient, the Black Fortress does seem to obey the Beast with great alacrity as if it is just an extension of his will—witness how the dome forms around Lyssa, or how the floor just so happens to crack open under the heroes, then close as Colwyn is trying to climb through. This would also explain why it collapses after he is killed. If it is an outer manifestation of the Beast's mind, its Malevolent Architecture would then be not only a typical Evil Tower of Ominousness, but a reflection of its master being an Eldritch Abomination (or at least, not thinking or viewing the world at all the way humans do).
Giant Spider: The crystalline spider guarding the Widow of the Web.
In the novelization, it's more of a case of Did You Just Romance Cthulhu??. The Beast says "You have been brought here for a marriage, though not of the sort you can imagine. It will be a much more intimate melding than you can conceive of."
Impossibly Cool Weapon: The glaive, a giant, telekinetic ninja star, with retractable blades. And manually adjustable rotation rate; Colwyn uses it as a rotary saw at one point.
He also seems to have so much appeal that a woman sent to seduce and trap him falls in love with him at first sight instead.
The Magnificent: Ergo, of course. (His "proper", full name is: Ergo, the Magnificent, Short In Stature, Large In Power, Narrow Of Purpose And Wide Of Vision. Though he will answer to just "Ergo" in a pinch.) He proves he isn't just comic relief in The Very Definitely Final Dungeon.
Meaningful Echo: "Only the king and his lord marshal carry those keys." The second time he says that, he realizes that Colwyn has made him his lord marshal.
Mood Whiplash: From bad to good — from another of Torquil's men dying by walls with Spikes of Doom closing in and the others in general peril to Lyssa and Colwyn happily meeting again. Also, a milder example in (paraphrased) dialogue:
Ergo: If I had my wish, I'd be out of this gloomy place...if I'd really have my wish, I'd be sitting on a gooseberry pie as big as a mountain. No, that's a bit greedy...I'll settle for one as big as a house. What'd you wish for, Titch?
Titch:(ponders) A puppy.
Ergo: Only one? Why not a hundred?
Titch: Only want one.
Ergo: Well, that's a foolish wish...what about you, Rell, what'd you wish for?
Pet the Dog: Literally, but inverted: the moment where it's first shown that Ergo has a heart and a more selfless side is when he turns himself into a dog for Titch to pet and hold.
The Power of Love: Which is considerably less metaphoric than in other examples. Part of the marriage ceremony in this story involves the female taking a literal fire from a ceremonial pool and holding it in her immune-to-this-flame bare hand. Lyssa literally carries this flame for Colwyn through the entire film until the Final Battle, where it proves to be more than the Big Bad can handle.
Princess Classic: Lyssa. Though in her opening scenes she shows courage, strength of heart, and more than a little independence (for one thing, it's made quite plain that the alliance by marriage was her idea and she bullied her father into it), and when she is captured it's clearly due to lack of fighting skills and training, not lack of desire to fight back.
Quicksand Sucks: In a surprisingly tense and desperate scene with one of the thieves. Considering this whole moment existed as one big distraction for the Beast to replace the Emerald Seer, the quicksand may well have been magically generated, thus explaining why it didn't act like the Real Life version.
Red Right Hand: Combined with Glamour Failure, the Beast and his servants could take any shape, but their eyes always looked demonic and evil. At least, when they opened their eyes, or used their powers in any other way. the one impersonating the Emerald Seer got away with it through the simple expedient of never opening his eyes when the heroes were looking at him, the one trying to seduce Colwyn only blew her cover when she manifested her claws.
Red Shirt: All but two of the brigands who join Colwyn, as well as all of the Slayers.
Refuge in Cool: The Glaive, the slayers' weapons, the Black Fortress, the Fire Mares, the twin suns, the cyclops, the translucent giant spider, and a marriage ceremony that gives the groom temporary but powerful pyrokenesis.
Rule Of Cool: Krull is a planet full of cool things.
Rule of Symbolism: Colwyn and Lyssa's love makes a literal flame that can destroy the Beast. The Black Fortress (evil) can appear anywhere. The Widow of the Web's hourglass sands not only can briefly stop time, allowing someone past the spider, but they also represent the span of her life—and thanks to Mindlink Mates, Yynr's too, so that spilling them ends their lives. Torquil not wanting to have his manacles removed until the end of the quest (when he'd earned it), only to keep them even after he does remove them as a reminder of the past he'd atoned for.
Shapeshifting Seducer: Or at least would-be lover, at two points. The Beast assumes Colwyn's form, and at least one of his minions can do so as well by impersonating the Emerald Seer. Whether the Changling sent to "make [Colwyn] betray her; if not, kill him" had a similar ability or was somehow assigned the form is not revealed.
Super Speed: Fire Mares can travel "a thousand leagues in a day." The definition of "league" differed according to era and location, but it refers to the distance a healthy horse can most efficiently travel in an hour - about five and a half kilometers. Fire Mares thus have a cruising speed of 231 kph or 143 mph!
Teleporters and Transporters: The Black Fortress vanishes from one location during a sunrise and appears in another (never the same place twice), to thwart enterprising young heroes. Figuring out where it will appear next so it can be intercepted is one of the major plot points.
The Walls Are Closing In: Includes the spiked walls version, and a gruesome death for one character who could have escaped but went back for his cherished knife.