Continuity mistake: In Season 2 Episode 22, Model Behavior, Woody has gotten his braces off. However, in this episode, he has braces back on again.
Land of Hold/Penny Henny - S2-E17
Deliberate mistake: When Garfield brings Jon to the broken TV, the scene's animation is still unrendered. (00:01:04)
Factual error: In the show Gaius wears glasses, except eyeglasses first came into use in the late 13th century while the legend of King Arthur is around the 5th or 6th century.
Triumvirate of Terror! - S3-E8
Continuity mistake: After breaking through S.T.A.R. Labs, Lex blasts Superman through a wall, leaving a human sized hole. He was on his back in the hole. When we see Superman again, the hole is shaped differently, and he is suddenly on his stomach. (00:06:50)