To the left of the bird is the Mad Hatter, who automatically triggers early in the game, after leaving the police station I think. He should already be listed. If you've made a mistake and it's the one to the right of the Bird, that requires game completion and all casefiles to be completed to trigger a completely uninteresting Most Wanted.
You are merely a master at word manipulation. BabaBzaa
The last most wanted is the Blackgate Escapees. You have to apprehend twenty of them.
A cautionary tale: it's possible to be locked out of this most wanted mission, causing an achievement and an unlockable batsuit to be unattainable.
When you complete the final case file, you should get a call from Gordon about the escapees. I didn't know this when I finished the last case file, and quit the game after it saved when I got the "all case files" achievement. Now, Gordon will never call me about the escapees, no matter how much I wonder around and do crimes in progress.
I thought, no matter, I'll get it on New Game Plus. I unlocked the escapees mission on New Game Plus, completed it, and got no "Clean Streets" achievement or bat suit. I have all sidequests complete on New Game Plus. I can never get the achievement on this file now as far as I can tell. ---