Continuity mistake: When Nadya escapes with her son from the monastery she drives the car through the doors, and the driver's side of the car sustains substantial damage at the side of the hood with the side-view mirror completely broken off, but during the chase there's little damage to the car's body and the driver's side-view mirror is now dangling at the side.
Continuity mistake: The damaged headlight of the car in which the kid and mom are running at the start switches sides. In the first shot when the car breaks through the door it's the left headlight that's not working, but on the road it's the right headlight that's not working. (00:03:30)
Continuity mistake: During Nadya's escape from the monastery, there are exterior shots of Nadya through the windshield and there's nothing hanging from the rear-view mirror, but in the interior shot (viewed from the back seat) just as she swerves away from the red car, there's a small cross on a cord which is hanging from the rear-view mirror.
Other mistake: As Johnny looks down on the wrecked car after defeating the devil, we see a blank brake disk without a wheel on. I guess it would theoretically be possible for all five lug nuts to rip clean off during an accident and leave the brake disk bare and exposed. But then the threads in the disc would still contain the shorn-off remnants of the lug nuts, instead of being empty. (01:23:00)