Deliberate mistake: After it is revealed Won-hyung has taken over Yeom's body, he is shown walking alone on the street and says aloud "She's not afraid of going to Hell? I can't make it so easy for her. Will she be able to leave behind the person she's been pining for so easily? I can't wait to watch the heart-rending sight." There is no reason for him to say this out loud. He is alone and not talking to anyone. The only reason he is saying this is so that the audience knows his plan. (00:33:23)
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)
Deliberate mistake: Although it was done for plot purposes, no school photographer would only take just one shot of a class photo. They generally take up to 15 to 20, as it is difficult to get everyone to look at the camera and smile at once (and hopefully not pull silly faces).
Deliberate mistake: When Fluttershy is telling off the cockatrice, her back legs and her wings turn to stone. But when she gives it the stare and the camera is right in her face her wings are outstretched.