Continuity mistake: The egg timer in the jail is about to run out, but when Dale runs over to it and tries to turn it over, there is more sand in it than before.
Continuity mistake: There are a couple of instances in the movie where the models do not correspond with the actual sets. When Klytus arrives at the Hawkmen city he lands near the top of the city. Yet in that very hall there is a pit with a deep void underneath. Such a room could only exist at the bottom of the city. Also, when the Hawkmen start to land on Ajax, its engine section appears to be missing. (01:10:10 - 01:14:30)
Revealing mistake: When Biro stabs the Imperial soldier with his sword, it's obvious that the sword is angled to miss his body. (01:30:50)
Continuity mistake: Several small meteorites are shown falling to earth. Two of them land in water, but only one of them creates steam. (00:05:10)
Revealing mistake: When the Hawkmen city is destroyed, you can see the lower portions of it wave about, revealing that it is in fact a model. (01:20:15)
Other mistake: The scenes with Flash and Aura in the shuttle are a complete mess. She tells him that the left lever controls direction, the right controls the altitude. When they are passing the planet Aquarius, she tells him to take a left turn over Fridgia. A) They are passing Aquarius at the time, not Fridgia. B) He moves the right lever instead of the left lever. C) The craft doesn't change direction or altitude and even if it had moved left as supposed to, they would have ended up crashing into Aquarius. The scene when Flash wants to talk to Dale is even worse. He pulls down the left lever to dive into Fridgia. It is the wrong lever. Then when he pulls back up, he correctly uses his right hand, but the right lever is already in the up position as seen in the previous shot. (00:42:15)
Revealing mistake: Just after Klytus has his sticky curtain call, and King Vultan orders the evacuation of the Sky City, watch for the wide shot with the fleeing Hawkmen superimposed in the background. As Vultan tells our heroes he and his men have too much to carry to give them a ride, watch his entire multitude of brave fleeing Hawkmen suddenly disappear one frame before the next shot cuts in.
Other mistake: During the battle for War Rocket Ajax, an Imperial soldier is shot by a Hawkman, but falls down after he should have done. (01:29:05)
Continuity mistake: As the Hawkmen evacuate the city, all the furniture is seen neatly assembled. When Ming arrives, however, the furniture is strewn all over the place. The only people who could have moved it would have been Flash's group, and why would they do that? (01:16:10)
Other mistake: When Flash and Vultan are watching the battle unfold on War Rocket Ajax, the rocket is seen moving forwards, with engines flaring, even though the captain has given the order for the engines to be stopped. (01:29:00)
Revealing mistake: When Flash is rescuing Barin from falling into the void, he rubs against one of the spikes and it bends as if made of rubber. (01:12:55)
Continuity mistake: Klytus is killed when he falls onto three spikes on the platform. In subsequent shots, the spikes that have pierced his body are gone. It can be most seen a minute later into the film, when the platform tilts upwards. (01:15:15)
Continuity mistake: When Flash is restrained in Ming's dungeon, he has a spiked headpiece on, preventing him from seeing. The spikes on this headpiece change position from shot to shot during this sequence in relation to his tied-up arms - i.e. the headpiece keeps being turned, and then is back in position again depending on the shot.
Continuity mistake: The colour of the lighting shining on the archway wall behind General Kala changes from white to green. (00:41:40)
Continuity mistake: When Flash, Dale and Zarkov first land on Mongo, the shots from inside the ship show Ming's guards walking right up to the ship's window and looking inside. When it then cuts to an outside shot, the guards are much further away.
Revealing mistake: Just after Vultan evacuates War Rocket Ajax leaving Flash on board, there is a shot of the rocket heading towards the camera. There is a green-tinted box surrounding it that the special effects team forgot to remove, after it had been rendered against the background. (01:36:05)
Continuity mistake: When the Barron and Flash are fighting with the whips, they hit each other and cut each other on the arms, hands and face, but in the scenes after the fight, neither one of them have so much as a scar where they were once cut.
Continuity mistake: When Barin and Zarkhov are listening to the Colonel on the video screen, the smoke from the control console appears and disappears between several shots. (01:36:35)