Deliberate mistake: In Series 1 episode 1 Nick can use a laptop fluently, yet in series 1 episode 2, Nick has to ask where the "." button is.
Snow Place to Go/Dunce Upon a Time/Gems the Breaks - S2-E4
Deliberate mistake: Dunce Upon a Time: When Lumpy falls off the beanstalk and hits the ground, his left antler is missing. Probably done deliberately so that his head could fall flat on the ground. (00:14:03)