Goofs

When Colwyn and his allies see the Black Fortress they intend to attack he says, "It's almost dawn - we must get inside before the twin suns rise!" But the sky is blue with white clouds. When they then ride up to the fortress, it repeatedly alternates between twilight and daylight.

When the "Fire Mares" first appear they are shod, but a later close-up of their feet (with fire) shows them unshod.

During the battle in the swamp at 46:20, a Slayer is hit by Rell's trident which embeds itself firmly in the creature's chest. And yet, in the following shot showing the Slayer sinking into the swamp, the trident is gone.

In the film a character claims that the planet is known as Krull and the main villain of the movie is named "The Beast". But in a 1997 interview with writer Stanford Sherman he stated that Krull was the name of the villain and the planet on which the movie takes place was known as Beast World.

When Rell the Cyclops is being crushed supposedly between two solid walls, there is no blood, internal organs or any other mess that one would expect to see.

When the "Fire Mares" appear, it is obvious that some are not mares (female) at all, but some are geldings and at least one appears to be a stallion (males).

When Ynyr comes back from the Widow of the Web and declares "At sunrise the Black fortress will appear in the Iron desert!" he falls over. As he does so he damages the 'rock' he is standing on, revealing the polystyrene it's made from underneath.

In a shot where a tiger is following Titch inside the Black Fortress, the horizontal "wipe" edit is plainly visible, revealing the two were not together at the same time on that set.

In the first shot of the Black Fortress, the film is being played backwards as shown by the smoke from the burning torches trailing in the wrong direction. Later the same shot is re-used but played forwards, showing the Slayers returning to the fortress after they have kidnapped Princess Lyssa.

It's clear many of the shots of Colwyn catching the glaive one-handed are actually him throwing it played in reverse.

At 13:00 Colwyn jumps onto a stone water basin. As he lands on the edge, big chunks of what seems to be painted plaster flake of a column, revealing a whitish substructure that looks like polystyrene.

At the end of the movie when Colwyn, Lyssa and their colleagues escape the dark fortress and begin climbing down, the fortress starts to break apart and gets sucked up into the sky. Then the very next scene shows the group running through a field a mile or more away from the fortress as it is still breaking apart just moments later. This would not be possible, since it would take much longer than a few moments to climb down the fortress and run an entire mile away.

When the bandits corral the Fire Mares in the canyon the waving arm of a crew member briefly pops out behind a rock in the distance (at 1:22:00).

At around 19:30 Colwyn scrambles along the side of a barren slope with very distinct features. This is followed by a rock fall scene in a very long grassy ravine as well as a climbing montage containing sheer cliffs and ledges. All these shots suggest that Colwyn has tackled a considerable distance. And yet, at 22:00, he is seen standing barely a few metres above the first slope described here.

When Menno sinks in the quicksand, nobody throws a rope out to him, despite at least one of the brigands (Nennog) having a big coil hanging from his belt.