Revealing mistake: When Elly is "skating" on the black oil while fighting the bad guys, we can see that it is Bryce Dallas Howard's stunt double in a few shots where it briefly shows her face.
Revealing mistake: When Constance's baby is taken out of the water, she is an obvious doll who doesn't wink or move a single inch. She even cries, but her mouth doesn't move. In some shots, she is replaced by a real baby.
Revealing mistake: We see Caesar's Palace in 1966. There are 1970s and 1980s cars in the driveway.