Character mistake: Brock states that the Diglett are plowing the ground and the Dugtrio are planting the trees, but the opposite is true (The Dugtrio are plowing, and the Diglett are planting).
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.