When drowning the witch using the dunking machine, the witch appears to be in no danger of drowning. The water never quite reaches her head.
During the car chase with the police and Van Helsing's car, a motorcyclist wearing a hat appears repeatedly in every shot.
That is no mistake, it's an intentional running gag. Clearly visible in a sequence where at first the motorcycle is passing by, then (after a nearly invisible cut) it is followed by the grey police van, then (after another invisible cut) Von Helsing's yellow vintage car, and behind it again the motorcycle.
A restaurant next to the road is shown in 2 different occasions with a sign that says "RISTORANTE Rinaldo". It is the Italian word for restaurant and an Italian name, respectively. However, they are supposed to be in Romania.