Yes Sir, That's My Baby - S1-E19
Continuity mistake: In the scene in bus station, when Mork is talking to the drunk sleeping person, he's holding a bag, there's a shot of the FBI man, and the next shot of Mork, he's not holding the bag anymore.
A Case of Overexposure - S5-E8
Continuity mistake: In season one episode 16, Arnold says that him and Willis never met their landlord. In this episode they remember him as Mr Darcy - when they see him they recognise who he is.
Continuity mistake: In the control room during the interview, one shot shows Johnny Fever without glasses, next shot in same scene, he has his glasses on.