Problem
I. It must be a new villain, and yes, it must fit within the Batman universe! It can connect to current Batman villain, it just has to be new.
II. It must somehow build upon/connect to a current issue within our culture like Batman always does.
III. You must develop a backstory for the villain (i.e. why are they a villain?! What makes them one? Where they born evil? Do they straddle the line between good/evil? Did something happen to them?).
IV. They need a costume -- what does it look like? Do they have powers? What are they? Do they travel with a posse? Or a companion?
V. What makes them who they are in other words what makes this villain "unique"?
VI. Create some tag lines/quotes that your villain would say.