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: Inside Toth-Amon's icy castle, just as the heroes climb up onto the steps from the water, only the thief is soaking wet as he emerges; the other heroes seem to be relatively dry.
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. (01:19:20)
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.
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.