Factual error: When Howard is running after the bouncy ball he is on the second floor of the Mall of America, however, you see him run through the LEGO store which is located on the lowest floor of the Mall of America, which is impossible if he was on the second floor before.
Continuity mistake: Throughout the scene where Jamie and Howard are in Jamie's room, as Jamie is drawing, keep an eye on his picture. It is inconsistent between shots.
Continuity mistake: When we see Howie reach his hand to pat the reindeer, he is clearly wearing gloves. As the reindeer snaps at his hand, we see he is no longer wearing gloves.
Continuity mistake: When Howard is first talking to the Santa in the department store the Santa tells him to "Have a little respect for the suit" then part of it slides off like it was glued on. He then sticks it on again. Problem is, when they are fighting at the conmen's hideout, he takes him down by pulling his beard - that is now held on by an elastic cord and snapping it back. Granted it is not the same scene, however the only thing that happened between these two shots is them driving to the hideout and he would have had no reason to change it.
Continuity mistake: In the scene where Howard is 'going to work' and Jamie is trying to talk him into staying, at first the cereal bowl has only a little bit of cereal. Then in the next shot, it is almost full again.
Factual error: When Howie's (Arnie) vehicle breaks down, he's on a landmark bridge in Minneapolis, crossing the Mississippi River at Nicollet Island. He's at essentially Zero Hennepin Avenue, Minneapolis, as the river is the dividing line between East and West Hennepin. He pushes the car off the end of the bridge and rolls to a stop at a diner. This is the landmark Mickey's Diner in downtown Saint Paul, some ten miles away, the one located at 36 Seventh Street West. Howie should have looked even more exhausted than he appears in the film.
Continuity mistake: In the scene with Sinbad and Howard in the radio place, Sinbad gets enraged, then throws the package (thought to be a bomb) and Howard hits the deck. The package lands at Howard's head, but in the next shot, it's way over to his left.
Continuity mistake: Howard knocks the wiseman's head into the fire. In the wide shot before he notices, the head is no longer in the fire, but in the next shot, it is once again in the fire.
Continuity mistake: In the scene, when Liz (Rita Wilson) is making cookies, Ted (Phil Hartman) comes in. In the shot, when she is scooping the cookies off the baking tray onto the plate, she only has 1 on the plate. The camera then goes to Ted, and in the next shot, nearly all of the cookies are on the plate. How could she have done that so quickly? They were so neatly arranged on the plate, and none were broken.
Continuity mistake: In the scene where Howard is in Ted's house stealing the Turbo Man doll, and he catches the wiseman on fire, we see a shot of carollers outside. The ground is covered in snow and the sky is overcast. Howard then kicks the wiseman's fiery head out the door in the direction of the carollers, and the carollers scream and run away. It is now sunny outside and most of the snow is melted.
Continuity mistake: When Howard is breaking into Ted's house he uses a credit card to get in. The camera shows a close up of the lock and door knob from the inside twice, both times you can see that the door is not shut properly.
Continuity mistake: At the end of his jetpack flight, Howie is diving headfirst straight down towards the ground. Then when the camera changes shot to see his landing, he hits the ground at a completely different angle, on his back. Furthermore, he suffers no injuries - that costume must be very well padded.
Continuity mistake: During the parade you can clearly see trees in the background with plenty of green leaves.
Continuity mistake: At the part where Howie is in the neighbours' house "stealing" the Turbo Man the head of a statue catches on fire. He tries a couple of times to get the fire out. In one shot the head is right next to his foot and in the next shot the head is gone. Then in the very next shot the head is back and he kicks it out the window.
Factual error: We see Jamie at his karate graduation as a yellow belt. In the scene where his dad apologizes for missing it, he picks up Jamie's new belt, which is purple. Although the order of belt ranks varies by discipline and by dojo, it is highly unlikely that any sensei would have yellow belt (which is almost always the second level) followed by purple (sometimes as low as the fourth ranking, but more often up to the seventh or eighth rank).