Dungeon Dice Monsters: Part 2 - S1-E47
Revealing mistake: When Devlin is typing into the keyboard, none of the keys are shown moving when he presses them. (00:14:59)

Starring: Eric Stuart, Amy Birnbaum, Dan Green, Darren Dunstan
Genres: Action, Adventure, Animated, Family, Fantasy, Thriller
Dungeon Dice Monsters: Part 2 - S1-E47
Revealing mistake: When Devlin is typing into the keyboard, none of the keys are shown moving when he presses them. (00:14:59)
Duel Identity, Part II - S1-E30
Character mistake: Yugi mistakenly says if he doesn't get a monster out to defend himself Mai can attack him directly, which wouldn't be possible since the rules of Duel Monsters during the Duelist Kingdom arc forbade direct attacks on defenseless opponents. That rule wouldn't be implemented until the Battle City arc.
Seto Kaiba: I'm surrounded by superstitious nitwits.