Continuity mistake: Near the end, Thomas is saddling a horse. He throws the stirrup over the saddle so he can cinch the girth. But he is interrupted by the presence of the witch he loves. Somehow, the horse has had its girth cinched and the stirrup is in its proper place, all without Thomas' help.
Revealing mistake: About seven minutes in, during the scene where we see Cooper helping the Nerd as a cameraman, you can tell that Cooper has been added to the scene using green-screen effects, as the actor was unavailable to shoot at the location. The lighting on Cooper doesn't quite match the lighting of the scene, and you can see a slight "blur/feathering effect" around him where the greenscreen background was removed.
Revealing mistake: During the opening, one of the shots showing infographics about the stolen diamond lingers long enough to allow the viewer to spot the most obvious kind of filler text - literally the "Lorem Ipsum."