There are a total of 28 playable characters that are confirmed so far for Injustice 2.
The characters that are available so far are Batman, Superman, Wonder Woman, Supergirl, Aquaman, Atrocitus, General Grodd, Deadshot, Harley Quinn, Flash, Blue Beetle, Bane, Poison Ivy, Brainiac, Robin, Black Canary, Swamp Thing, Catwoman, Cheetah, Cyborg, Dr. Fate, Green Lantern, Firestorm, Green Arrow, Black Atom, Captain Cold, Scarecrow, and Darkseid.
It is worth noting that Darkseid is a character that will only be available as a pre-order bonus for now. The revealed Power Girl, Reverse Flash, and John Stewart’s Green Lateran are nothing more than special premier character skins with a new look, voice, and dialogue. The previously mentioned characters are special character swaps for Supergirl, Green Lantern, and Flash. A total of nine dlc characters are to appear in Injustice 2; but there is no information regarding who will make the cut.
Injustice 2 Trailers