Revealing mistake: When Clark (on the saucer sled) reaches the bottom of the snow hill, and is on the highway, as the headlights of the truck are coming at him and the "sparks" are flying from under the sled you can see the wheels underneath to make it roll across the highway to reach Walmart's parking lot.
Continuity mistake: The entire Christmas bonus scene at end, Clark's tie changes. Take note of the pattern on the knot, which changes from shot to shot.
Factual error: When Clark is sliding on the saucer, he shoots out a shower of sparks when he crosses the street. Those old saucers were made of aluminum, and aluminum can't create sparks like other metal does.
Continuity mistake: When Santa Clause's sled passes in front of the moon at the end, why is the sea so dark? It wasn't in previous shots.
Chosen answer: Because there was cat food in her jello mould. He's pointing out the absurdity of someone adding cat food to jello.