Revealing mistake: In the recap, in the wide shot where Mr Freeze uses his freeze gun on Batman and Robin, you can see they are stunt doubles.
Visible crew/equipment: When the photographer is getting a picture of the princess, you can see the shadow of the boom mic on him.
Other mistake: During the final fight scene between the SOCK and POW, Mr. Freeze can be seen in the 76-degree heated section.
Answer: There were three well-known actors who played Mr. Freeze, each one a different height, weight, and physique. As these were notable guest stars, the costume designers would adapt the costume to best fit each actor who likely would want to avoid comparisons to the other Mr. Freezes, incorporate their preferences, as well as refresh the look, rework whatever didn't work in previous versions, and so on.
raywest ★