Artistic License - History/Military: 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.
The 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.
Deal with the Devil: The cyclopes, in their backstory. They were once normal humans living on a distant world. They made a deal with the Beast, exchanging one of their eyes for the ability to know the future. The Beast cheated them, however, only allowing them to know the times of their own deaths, and ensuring they will die horribly if they try to resist their deaths.
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.
I Know Your True Name: Ynyr is able to reach the Widow of the Web by calling her true name, Lyssa. It is a coincidence that she has the same name as the princess.
This troper has always read that as There Are No Coincidences: the Widow and Ynyr were, in their youth, potentially the ones who would fulfill the prophecy, but lost the chance when Ynyr abandoned his Lyssa and she killed their child in retribution—and that was why the Widow was serving such an awful penance for what was a horrific, but ultimately small, personal crime in the grand scheme of things. (And, possibly, why Ynyr was fated to help Colwyn in his quest, though Ynyr was unaware of what the Widow had done.)
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.
Inept Mage: Ergo. Until he realizes he doesn't have to polymorph others.
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.
Mars Needs Women: The alien Big Bad, the Beast, kidnaps the hero's fiance. Although it is less that he needs a woman and more that he wants to deprive Colwyn of his to protect himself from theirpower.
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.
Men Act, Women Are: Lyssa gets kidnapped and provides Colwyn with the drive (and power) to succeed; the Widow provides the information they need to find the Fortress but otherwise does nothing. All other roles are filled by active men (save the Seer).
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?
They are very powerful though, easily slaughtering the Redshirt Army near the beginning of the movie, and even the heroes have a difficult time fighting them. Thus they could be considered Super Soldiers.
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 the kingdom soldiers in the first part of the movie.
Rule of 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 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.
Science Fantasy: It's basically a fantasy world invaded by high-tech aliens.
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.
Torquil: Fame? It's an empty purse. Count it? Go broke. Eat it? Go hungry. Seek it and go mad!
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.
Too Awesome to Use: The glaive. The hero is specifically told not to use it until he faces the Beast. Otherwise the movie would just be a long string of monsters getting hacked apart by a flying rotary saw.