Character mistake: Professor Saotome checks the status of the Getter Robot when his son falls unconscious. The HUD output is written in awkward EngRish, from the first line of the status report, called; "Monitor the state of affairs", to smaller details like the article randomly used for certain lines ("a control device, a correspondent"). The biggest flub though is that the name of his son is "Tatsuhito", in proper romanization, but here appears as "Tatuto." (00:05:20)
Character mistake: In s01e08, "Q and A", Yelena moves her bishop to B6. The announcer says that's going to win it (the game gets interrupted at this point). However, that move does not put the computer (her opponent) into checkmate, it doesn't even put it into check. Her bishop is on a dark square and the computer's king is on a white square.
Breaking of the Sacred Seal - S3-E23
Character mistake: When Marcel activates his two face-down cards, he says "I'll start by revealing my two face-down cards which both happen to be Break the Seal spell cards", but they are trap cards as they are pink and spell cards are green. (00:15:10)