Revealing mistake: When the UFO makes the huge flash that knocks everyone in the cemetery down, one of the police officers kicks a tombstone as he falls and it wobbles back and forth. (00:13:35)
Factual error: Maleficent states that Princess Aurora will prick her finger on a spindle - the part of a spinning wheel that holds the bobbin. Spindles aren't sharp; what Aurora actually pricks her finger on is the distaff, which is used to hold the fiber before it is spun.
Continuity mistake: When Wilby goes into his bedroom, he takes out his PJ's from the bureau drawer, leaving the drawer open. He goes into the bathroom to put on the PJ's. When he comes out of the bathroom, the drawer in the bureau is closed.
Other mistake: When the Behemoth swims up the river & capsizes the ferry, a static model is used that bears no resemblance to the animation model seen throughout the film.
Factual error: Karnak was an Egyptian city, not one of their gods.
Revealing mistake: When Holmes kills the guineapig-human hybrid, the entire scene is ridiculous. In the first shot, the guineapig has tiny human hands that look to be about a half-inch at most. Holmes then steps on it, and in that shot it appears to be a different type of rodent entirely. Then we see the human hands under his shoe flexing in pain, and they look to be significantly bigger than before based on the scale of his shoe... at least 5X bigger than they were.