Continuity mistake: In the last scene, the Butler and Groomsman load a Sarcophagus in the back of their station wagon. The tail gate is left open and both step back as the vehicle pulls out. As they are driving off down the driveway the tail gate is closed.
Visible crew/equipment: In the bar fight scene, the camera crew is visible right after Lefty hits one of the bar patrons.
Continuity mistake: When Ira and Glenda are discussing Nick, who is hiding under the bed, Ira briefly stands on Nicks right-hand pinky finger. After Ira has walked away, under the bed Nick grimaces while holding his left-hand pinky finger.
Other mistake: David is trying to locate the beast through a map of the city - for some reason, since he already located it before. Problem is, the movie is set in Missouri but the map he's looking at on his bed is a map of Los Angeles (you can even read "Granada Hills"). Similar mistake a few minutes later in front of the sewers; you can easily read "Monterey Park" to the right of a different map he props against the wall. (00:37:15 - 00:38:35)
Plot hole: When the gang goes to retrieve all the cars from the guy living in the desert they determine they have enough cars for a a one car safety limit. As they discuss this Jim is measuring the length of the blue car Jeff will be driving but the license plate of that car is never taken into account when being measured, so they should have already known that even with enough cars in their possession they didn't have enough cars to make a mile.
Suggested correction: They had a one car 'cushion", but it wasn't the blue Mercury, it was the car on the trailer the Jeep was towing. They had just enough with the Mercury, but he crashed it coming into the parking lot which shortened it ; the plate falling down added the extra inches.
Audio problem: The sound of a punch Tommy throws during her match with Princess War Star occurs before the punch connects.
Factual error: When the Peanuts gang got to Victoria station, Travel Center is spelled the American way. Since it's England it should be "centre" (00:24:55)
Revealing mistake: Linderman refuses Clifford's offer to be his personal bodyguard from Moody's gang, and leaves. As Clifford walks by the students practicing their violins, playing Mozart, their bow movements do not match the music.