Continuity: Several scenes supposedly occurring in the same location were obviously shot on different sets. This is because the shots involving American actors were shot in the USA, whereas the shots involving Spanish actors were shot in Spain.
Audio/visual unsynchronized: Spanish actors.
Incorrectly regarded as goofs: Normal slugs don't have teeth, but these are mutant slugs.
Continuity: Mike Brady says a line before he's supposed to. Towards the end of the movie, he barges into the commissioner's office and tells the secretary, "Will you tell Mr. Phillips that Mike Brady is here to see him?" The secretary replies, "Hey, his office is closed." Brady says, "Yeah, watch me!" but only then the secretary says, "You can't go in there!"
Continuity: When Mike Brady and the sheriff are driving down the road in the police car, the camera on the driver's side clearly shows that Brady's window is rolled up, but in the next shot over on the passenger's (Brady's) side, he throws his cigarettes out the window.