Visible crew/equipment: When Lionel returns to the jazz bar and discovers Billy Rose has been killed (framed as a suicide), you can see two people standing in the shadows to the left of Lionel as he enters the main room where the stage is located. A man is hunched over, whilst a woman is standing still wearing what looks like a dust mask. (01:32:27)
Continuity mistake: When Joker confesses that he was the one who killed the three guys in the subway at the Murray Franklin Show and also says "It's not a joke", he keeps his gaze turned towards Murray in one shot and towards the audience in the next.
Continuity mistake: When Russ and Frank are in the hotel pool the woman in the left is holding a cigarette. In the close-up it swaps to a lemonade. Then in the wide angle it swaps back to a cigarette.
Visible crew/equipment: As the camera moves forward in the opening shot, a clear reflection of a film light can be seen on the side of the fire engine.
Other mistake: Elsa Brecht is holding an official piece of mail sent from the Coconut Grove Hotel in Miami but it's postmarked Orlando, Florida. There's no legitimate reason the mail would be postmarked Orlando when Orlando is 235 miles from Miami. (01:24:16)
Continuity mistake: Young Shaft is meeting his friend at the bar: he has just his solitary drink before him when Karim arrives, but the drinks are now 2 with Sasha's arrival - only for a single shot, though, as just a single glass is afterwards. (00:11:40)
Continuity mistake: En route from the front door of Wayne's mansion to the table in the Batcave, the pile of pizza boxes in Alfred and then in Mike's hands continues to change in size and number: at first the pizza girl delivers 11 boxes, Mike slams on the table just 8, but he brought down the stairs twice that amount (without counting through freeze-frame the precise numbers, it's simply obvious at first glance that the pile is bigger in some shots and the pizzas themselves are pictured of inconsistent size).