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.
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.
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.