When the group of friends first open the suitcase they find in their new house, there is no orange-striped shirt inside at first, yet it suddenly appears out of nowhere when they open it again to examine its contents.
The Sheriff and Marge the Dispatcher, despite being law enforcement officials, are clearly not wearing anything resembling a police uniform.
The goblin's costume is very visibly coming apart in several scenes, to the point where you can plainly see the actor's sneakers.
The Sheriff blinks in the closeup shot of his corpse, even though he's supposed to be dead.
The "radio" in the Sheriff's police car is obviously just a telephone prop.