Continuity mistake: In some episodes like Trial the inmates are wearing prison uniforms while in others like Fear of Victory they're wearing their costumes. Another thing is the prison uniforms constantly change color, in some episodes they're light grey, others light blue, then in some light purple.
Continuity mistake: The Joker reads “Charles Michael Collins” from Charlie’s card, but later, when he shows it to the camera, there is no middle name on it.