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.
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: 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: During Conan's sword-fight with one of the Queen's guard (after the escape from the castle), you can tell the sparks were added in afterwards. At one point, Conan's back is to the camera and the guard attacks from Conan's front and a spark is seen in front of the back of Conan's head when his head should have blocked the view of the spark.
Revealing mistake: When Conan's assistant Malak is climbing down the waterfall, he causes some rocks to fall, one large one obviously lands right on him, but he is fine in the next shot. (01:24:15)
Revealing mistake: Just after the fight between the tied woman versus the 6 men she jumps on a horse and starts going up the hill. At that moment the camera moves sideways while showing the back of people's heads, in a hat you can see the information label (make, studio etc.).
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.