Continuity mistake: At the beginning of the film in the scrapyard, we are shown a car suspended by the grab crane. When the Juggernaut appears and all starts to go wrong, the same car drops and barely misses the psychic. Later, we once again see the car suspended in the grab crane.
Other mistake: When Dennis jumps out from behind the glass wall shield, leaving Arthur behind it and The Hammer and Juggernaut ghosts attack, Arthur bangs the glass yelling as if he can't get out; but the wall shield is only propped up, unsupported and should've fallen straight forwards when he thudded his fists on it.
Visible crew/equipment: Halfway through the movie (when the gears start moving) the glass doors begin to close. It appears that a set of four hands are closing them in the top portion of the screen.
Continuity mistake: In the scene where the psychic and the father are walking through the halls carrying the plate of glass as protection, you can see the trees outside blowing in the wind. Earlier, they showed that all the windows in the house closed up, making it impossible to see outside.
Continuity mistake: Near the very beginning of the movie, Arthur (Tony Shaloub) trips over his son's scooter and spills coffee on himself; throughout the scene, the stain keeps changing size and location. (00:13:10)
Other mistake: When Maggie puts the "magic" glasses for the first time, you can see that the light in the right (left to us) lens sparks and then turns off. In the next scene it works fine. (00:31:21)
Other mistake: In the scene where Cyrus's Nephew first sees the kids in the in the machine. (1:18:45) The shot goes back and forth from him to the machine. The first 2 time the glasses are fine the last shot (1:18:550 The prescription inserts in the glasses are crooked. Bad editing. (00:18:45 - 01:18:55)