Other mistake: In the beginning of the movie, when you first see Mary-Kate (aka Mel) and Ashley (aka Ally), Mary-Kate walks off without ever closing her locker.
Other mistake: When Hamm turns off the TV at the beginning, there's no reflection of him, Rex who is beside him, or the remote. (00:06:58)
Other mistake: When the agent shows the spiral for the pattern of the messages, the spiral goes through South America and America. But the agent, before, showed two messages that aren't in the pattern; one in England (Stonehenge), the other in Cairo, Egypt.
Other mistake: During Brown's dream, where he saves a runaway bus, Brown throws a hook, which latches onto the bumper. One shot of a middle-aged woman staring in awe was obviously done backwards, because the letters on the store behind her are written and spelled as such.
Other mistake: When Sly hypnotises the guy, he tells him to wiggle his tongue. He starts wiggling his tongue exactly when Sly says, "Wiggle."
Other mistake: When Ash and friends are first seen walking up stairs, Pikachu's tail is briefly mistakenly coloured brown with a yellow base instead of yellow with a brown base. (00:15:13)
Other mistake: It's reasonable to assume that the house can hide small things like posters and even shelves when projecting images on the walls. When Ben's two friends arrive for the party, one of the walls shows an image and the couch disappears, and that's just way too big of an object to simply phase away, given what we see that the house can do.
Other mistake: Throughout the film, the Hickams' phone buzzes. When Elsie throws the phone into the yard, it breaks to reveal a pair of bells.
Other mistake: When the Boogeyman gets hit with the plastic eye the Boogeyman flips over when the Boogeyman should have just fallen.