Continuity mistake: Charlie and Scott come across the empty Santa suit in the flashback to the first movie, and the body and all the limbs of the suit are flat in the snow. A shot from the unconscious Santa's right shoulder then shows his arm and gloved hand still upright and in position to wave "bye-bye" before he disappears.
Audio problem: When Scott is making a distraction, he says, "Well, this show stinks." But his mouth is saying, "Well, this show sucks." Done in order to keep the G rating, I presume.
Continuity mistake: The second time Jack and Santa fall from the sky and are laying in the snow outside the townhouse, it cuts to the scene from the The Santa Clause where Scott Calvin first puts on the coat. However, in the original movie, Scott doesn't put the coat on until after he and Charlie have left the townhouse in the sleigh and are on the roof of the first house in which Scott goes down the chimney.
Revealing mistake: When Neil is teaching Yoga exercises to the elves a first close up shot of one of the elves (the Asian looking one) shows he doesn't have pointed ears like the rest in the group.
Revealing mistake: When Lucy is going into the snow globe collection there is a spark reflected in her eye that goes over her eye lid, which shouldn't, that is a FX Problem.
Continuity mistake: About 8 minutes into the movie, there is a news rolling display in the background which is rolling from right to left which is normal for the English language. In a close-up of Mrs. Claus, she has an expression on her face and the news scroll is going left to right behind her which doesn't work for the english language.
Continuity mistake: When Neil is teaching yoga to the elves, you can see the Elf in the blue sweatshirt from the back with her sleeves pushed up, but when the camera is in the front facing the elves, her sleeves are down. (00:31:42 - 00:32:16)
Plot hole: After Jack Frost ceases to be Santa and Scott Calvin becomes Santa by putting on the suit, everything at the North Pole goes back to the way it was. Inexplicably, though, Lucy's parents, who had been frozen by Jack Frost, remain frozen.