Continuity mistake: When Larry is driving Kyle out of Darkness Falls, Kyle pulls a gun on him to get Larry to turn back to the hospital. The camera angle changes from a rear shot to a side shot a few times, during which Kyle goes from looking directly ahead without the gun raised to facing Larry with the gun raised. This happens a couple of times just before the tooth fairy flies in front of them and causes the car crash.
Continuity mistake: When the police are taking Kyle-as-a-kid after his mother's death he's stood by the car (looking fairly evil) with many bloody cuts on his face and neck, but the next shot of him sat in the car shows he has just the one tiny unrelated nick on his cheek he had at the beginning of the film before the Tooth Fairy's attack.
Continuity mistake: When Kyle, Kaitlyn, and Michael are going down in the elevator, the floor-indicator light switches from three to two. Then ten seconds pass, the elevator jams, and the light is still showing floor two. Pretty pokey elevator that takes more than ten seconds to move from floor to floor.
Continuity mistake: Throughout the movie where light is used to keep the tooth fairy at bay, her "sensitivity to light" seems to change a lot. A light stick that generates no heat and throws a dim glow keeps her away, but she'll come up close enough to a hot gas lantern to be decently illuminated.