Dragonslayer (1981)

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: In the scene right before the dragon picks up Ulrich, you can see the dragon pass through Galen and Valerian. (01:41:45)

Revealing mistake: At the beginning of the final battle, the dragon flies up toward the wizard and a sharp horizontal line breaks through the dragon, revealing the composited shot.

Tyrian: If he's ready to lay a dragon in its grave, he's nothing to fear from me.

Galen: Are there other entrances?
Valerian: No! One's enough.

Valerian: Is.
Hodge: Yes, this is Kragenmoor and yes, this is the house of Ulrich, and no, he won't see you.
Valerian: But.
Hodge: I know, you've come a long way, your business is urgent. It doesn't matter! He sees no one.