Revealing mistake: In the first person shooter sequence, when Reaper gets the chainsaw, there are many parts where he is moving it around near Pinky, now the beast thing, and it does not have a shadow, and at other times when it is at the same angle, it does.
Revealing mistake: When Loki disguised as the delivery person grabs the baby, he's replaced by an obvious doll, with pale yellowish skin and lighter hair colour.
Revealing mistake: In the beginning of the movie, at the scene in the morgue, dead David's eyelids very slightly shake right before his casket is closed. (00:04:20)