Revealing mistake: Julia confirms that Barnabas is a vampire by sneaking a look at him in her compact mirror - which reflects his human companions, but not him. Unfortunately, the producers seem to have forgotten that vampires don't reflect when, near the end, we see the recently-staked vampire Roger Collins - in a mirror. Not even "dead" vampires ever appeared in mirrors in the TV series, so they shouldn't do so here, either.
Continuity mistake: The wooden box (holding the "silver bullets" that the sheriff is handing out) has no markings on the side from a distance, but when the camera zooms in to see the ammo, you can see heavy black marks like someone crossed out a name and address, and you can also see a paper label partially torn off the box with writing blacked out. Then when the camera zooms back again, and the deputy picks up the box, the side of the wooden box is blank again.