Winning Through Intimidation - S1-E15
Continuity mistake: Panik's Metal Guardian can be seen on the field several minutes before he actually plays it. (00:10:30 - 00:13:00)
Duel Identity, Part II - S1-E30
Continuity 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.