Sinister Secrets: Part 2 - S5-E13
Continuity mistake: Leon uses his Cinderella monster's effect, which allows him to transfer Cinderella's glass slippers onto Dark Magician Girl's feet, causing her to lose 1000 attack points. Later, after Zigfried admits that the Golden Castle of Stromberg card is illegal, there is a wide shot of him saying, "The most powerful card never released is already on the field," and in the shot, Dark Magician Girl is wearing her blue boots and not the glass slippers. (00:13:02 - 00:16:45)