Continuity mistake: When Cheryl is running through the woods, she is wearing slippers that stay on up until she reaches the cabin door. However, in following shots, she is shown barefoot, and when Ash opens the door her foot is dirty as if she'd been running barefoot the whole time. (00:28:05 - 00:29:10)
Factual error: When the Titanic sinks all six dwarves and Kevin end up in the sea clutching a lifebelt. The water in which the Titanic sank was freezing - that is how most of the casualties died, by freezing, not drowning. In water like that you'd be lucky to stay conscious for more than a few minutes. Despite this none of them show the slightest effect of the cold. Maybe the dwarves have some 'magical' ability to withstand lethal cold, but Kevin doesn't even react to being plunged into freezing cold water. He'd be screaming in pain, but he doesn't even show the slightest sign of discomfort.
Other mistake: When the two Americans are walking on the moors, their shadows are always in front of them, despite them having changed direction numerous times. Additionally, with the moon always being behind them, how are their faces being lit?
Audio problem: During the climax of the film, the maiden takes the stone from Galen and attempts to smash the amulet. Galen pulls the stone away and says "NO! He said I'd know the time". However, his lips do not match the words. He appears to say "NO! It is not yet time!"
Revealing mistake: At the beginning when the ruler is making his speech, you can see his modern day fillings in his upper molars.
Visible crew/equipment: After Arthur drinks from the Grail and goes to visit Gwinevere at the convent and she gives him the sword back, he paces around her chamber- you can clearly see the film crew reflected in his armor.
Continuity mistake: When the two station reporters are showing Eddie's drawings to George Waggner, the drawings change position on the desk between shots. (00:16:00)
Other mistake: As Debbie walks through the foggy maze from her upstairs bedroom to the bathroom across the hall, she closes the door and then asks herself why she is in the kitchen, when the kitchen is obviously downstairs.