As much as I love Freeze, I just don’t want him in this story. He’s one of the worst characters to use as a main villain in what’s pretty much Act 2. It just comes off as fan service to me. You would have to shift gears and change quite a bit about his character just to fit him in. He would work better in a stand alone film, another universe or just not at all.
There’s plenty of other villains that make sense for the natural progression of the story.
There needs to be a new D.A., so it makes the most sense to use Two-Face. He’s literally the perfect villain to put in Act 2 where Gotham is rebuilding in the middle of a mob war/power grab that was stated at the end of the first film. For the war, you can bring in Black Mask, Rupert Thorne and/or a number of mobsters.
Someone needs to take over Penguin’s drug operation. Hatter could easily fill this position. I absolutely love this idea and it would be interesting for sure, but not necessary.
There’s the murder of Edward Elliot that can possibly lead to the rise of Hush.
You have the inmates at Arkham. So far we only know of Joker and Riddler, but there were a few other occupied cells. You also have Harley, Crane and Strange that could potentially work there.
Catwoman is definitely returning and there’s no telling what role she would play, but I would love to see her go up against her half sister Sophia Falcone.
That’s a lot going on already. The cheap and uninteresting way to bring in someone random as the main villain is to blame the death/tragedy of a family member on Riddler’s flood that led the villain to causing havoc. I say just build on what we already have and stick to it being an epic crime saga.