When Howard tears up the Turbo Man display in the toy store, there is a man leaving with a Big Bird in the background. The shot cuts away to another customer. When the shot goes back to Howard, the man in the background can be seen walking away from the point at which we last saw him, as if he paused while the camera was off Howard. Given the speed at which the man was traveling, he should have been farther along at that point.
When Arnold departs from his acerbic neighbor, apparently headed to downtown Minneapolis, the longshot that follows is St. Paul. Then there is a cut to Arnold running frantically through a crowd in downtown Minneapolis.
In the store on Christmas Eve morning, all the customers and salespeople laugh because there are no more Turbo Man dolls and they claim that the last doll went with a lady in a fur coat. But, if you look closely, you can see customers holding Turbo Man dolls and some on the shelves. However, the boxes they're holding say "Turbo Man" on the top to indicate they are associated with the Turbo Man toy-line. Boxes containing Booster and Dementor are in similar boxes, so they could very well be in the boxes held by customers at the toy store.
When Howard first arrives at the Mall of America store for the late Turbo Man dolls, he is going down an escalator. Then, in the next shot, a crowd is shown at a toy store. You can see Howard in the crowd before he even gets there.
When Howard is in the pay-phone booth at the diner, he was supposed to call "555-KQRS." He dials, "555" and then moves his finger to press the number "8" The letter "K" on a telephone is on the number "5."
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.
When Howie is fighting Giant Santa in the warehouse, after Giant Santa punches Mini Santa off of Howie, he punches Giant Santa. When he does this, Giant Santa's face goes in the opposite direction in which the punch was delivered.