The Simpsons Christmas Special: Simpsons Roasting on an Open Fire - S1-E1
Revealing mistake: After Homer brings Santa's Little Helper home, Homer and Marge hug, and if you look behind them, the background is upside down. There is a picture hanging upside down, and there is a lamp which seems to be hanging from the ceiling. Then in the next shot, the background is normal. (00:21:40)
Revealing mistake: When the first fight starts, the Bloober disappears into thin air. (00:04:52)
The Ringer - S1-E1
Revealing mistake: When Link calls down to Zelda from the tower, you can see a fault in the drawing as Zelda moves. There is a low wall around her on the balcony, with flowers and vines on it. As she moves, you can see some of her dress pass right through the wall and vines towards the lower right. (00:01:50)
Shanpû no hangeki! Hissatsu shiatsuken wa mimo kokomo ubau - S1-E16
Revealing mistake: In his close-up when he grins at Ranma after his request to help him figure out what happened to Akane, Ryoga is drawn really obviously with the hair going under his eyebrows. (00:15:00)