Revealing mistake: Conan and his party flee from the temple guards and escape into the crypt, closing the huge stone door behind them. A moment later, the camera shows the leader (Ferdinand Mayne) standing at the foot of the steps holding a torch. He chucks the torch out of sight to his right and begins walking towards the door. If you look closely you'll see the torch disappear nicely out of sight behind the wall as if he had "passed" it to someone standing there.
Continuity mistake: When Zula is fighting Bombaata, she leaps from the saddle and throws herself on him, knocking his head-circlet off from the impact of collision. In the very next shot, Bombaata's circlet is back on his head as he struggles with Zula.
Continuity mistake: Inside Toth-Amon's icy castle, just as the heroes climb up onto the steps from the water, you should notice that only the thief is soaking wet as he emerges; the other heroes seem to be relatively dry.
Other mistake: When Conan is fighting the Ape-man and his friends are watching behind the mirror, the cold air on their breath is actually cigarette smoke. You can see it swirling every time they speak. In one shot you can actually see Malak's hand move behind the other actor and he's holding the cigarette. I think this is why there are audio problems here, they had to dub the voices in because the actors couldn't speak with the smoke in their mouths. DVD viewing.
Audio problem: When Conan is fighting the half lizard/man monster and discovers that breaking the glass panes hurts him, it cuts to a shot of his friends behind one of the panes and the thief says, "That's exactly what I would have done, exactly." His lips don't match the words at all.
Continuity mistake: When Conan is fighting the half lizard/man monster, the first two times Conan smashes glass panes, you see large gashes appear across each of the monster's pectoral (chest) muscles. Later in the fight the wound on his right pectoral disappears and reappears numerous times.
Revealing mistake: During Conan's fight with the man-ape, at one point the man-ape grabs Conan by the ankles and swings him around like a whirligig. During this swinging, Conan's hair remains unruffled.
Revealing mistake: In both shots rowing toward the ice castle and back from it, the shot is obviously using some sort of rear projection, as the film running behind has marks such as hairs and scratches that have been amplified. The contrast between the main shot and the rear projection is different too.
Continuity mistake: When the Dagoth-monster manifests and kills the Queen, Conan is already covered in blood from having fought guards, but as the battle with Dagoth continues he gets progressively cleaner.
Continuity mistake: Two horsemen try to entrap Conan in a net during the opening fight sequence. He rolls under the net, grabs it and gives it a mighty heave, sending both horsemen sprawling, and then drops the net over Valeria's stone altar. A few shots later, the altar is bare and the net is nowhere to be seen.
Continuity mistake: Watch the shot where Bombaata is smashing a hole in the rock wall with his mace-axe weapon. From the outside it appears as though an entire section of the wall is giving way, then the camera cuts to Bonbaata on the inside and he is smashing at a rather small hole in the otherwise intact wall.
Revealing mistake: During the escape, through the tunnel, Bombaata caves the tunnel in. Conan then digs through the rock pile and crawls over them, while they bend like foam balls.
Revealing mistake: In the opening credit sequence, as Conan and the rest are galloping triumphantly across the mighty windswept plains of yore, you can see power lines in the background.
Other mistake: When Conan etc. are walking through the ice palace looking for the princess, not only do they miraculously dry off, but not one of them gets goose bumps, even though it is cold enough to fog up their breath.
Continuity mistake: At the start of the film, Conan is attacked by several horsemen. As the first one comes riding past him, he grabs the man from the saddle and flings him to the ground. The next shot shows that same man flying through the air screaming.
Continuity mistake: At the start of the fight in the temple, Conan throws his dagger and kills a soldier. The huge fight kicks off and the heroes collect the jewell and escape up the secret passage. When Conan remounts his horse, the dagger is in its sheath in his belt.