Two Plumbers and a Baby - S1-E17
Continuity mistake: Normally, the castle has a door, but when King Koopa says that the infants will have to do all of his chores, the door disappears. This also happens when Luigi is trying to listen in on what is happening inside the castle. (00:06:05 - 00:06:27)
Two Plumbers and a Baby - S1-E17
Continuity mistake: When Mario says that they have to free the children, his black sideburns turn red, like his cap. (00:06:43)
Two Plumbers and a Baby - S1-E17
Continuity mistake: In one scene, Luigi is wearing the same color hat as Mario and when Luigi opens his mouth to talk, it's Mario's voice we hear.