Revealing mistake: In the scene where Lancelot runs into and fights Arthur's ambushers, he runs one of them through with his sword. It is visible that he stabs his opponent past the body, but close enough for the appearance.
Revealing mistake: When ice is shedding from the plane's wings, the chunks slowly slide forward and then down the leading edge. Loose chunks should have flown off rapidly to the rear due to the airflow.
Revealing mistake: At the end, when King's troops are attacking Khan's camp, a "dead" insurgent hops up and runs off screen just as the arsenal explodes. (01:36:00)