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 "going to work" and Jamie is trying to talk him into staying for the Wintertainment Parade, at first his cereal bowl has only a little bit of cereal. Then in the next shot, it is almost full again.
When Howard tries to pet the reindeer, he is reaching for it with his right hand, wearing gloves. In the next shot from his point of view, a left hand with no glove is reaching for the reindeer's head. One shot later, he is suddenly pulling back his right gloved hand.
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 the customers at the toy store are in a rage when Howard shouts that Myron grabbed two balls, they go wild and they make the ball drop out form Myron's hands. However, there was no guarantee that the ball that bounced away was the winning one.
When Howard is in the pay phone booth at Mickey's Diner, he was supposed to call "555-KQRS." He dials "555" and 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 we can see the door is not shut properly.
When Howie is fighting the Giant Santa in the Santas warehouse, after Giant Santa punches Mini Santa off Howie, he punches Giant Santa. When he does this, Giant Santa's face goes in the opposite direction in which the punch was delivered.