The Seventh Shadow Rider - S1-E44
Continuity mistake: After Professor Crowler's science experiment goes wrong, he starts shouting and it cuts to a shot of the students laughing. In this shot, Alexis and two other Obelisk Blue students can be seen behind Jaden, Syrus and Chumley laughing. Then it cuts to a shot focusing on Jaden and Syrus, and Alexis and the other students behind them have disappeared. (00:03:39)