First up is Bluebird, aka Harper Row.
A recent addition to DC's comics, having only been introduced during Scott Snyder and Greg Capullo's Batman run from the New 52, Harper went on to become an important member of the Bat-Family, before her superhero identity was fazed out in DC Rebirth. Given Injustice 2 released just as Rebirth was gaining momentum, it's easy to see why they didn't use the character in the end - particularly when they had so many Batman characters to use already.