NetherRealm Studios' Ed Boon recently tweeted out a darkened image of what appears to be a Hyena with the text, "A couple of fun reveals coming soon for Injustice 2,” and, “Gamescom: stay tuned for reveals.”
A couple of fun reveals coming soon for Injustice 2pic.twitter.com/OAc40RmyqO— Ed Boon (@noobde) August 16, 2016
Harley Quinn, who was playable in the original Injustice, but has not yet been confirmed for the sequel, has a pair of pet hyenas. It's entirely possible that one or both of the hyenas could be playable fighters in the game, but I have my money on them being present to lend Harley Quinn a violent hand. It's also possible that it might be a tease for Joker, another fighter from the original game who has not yet been confirmed for the sequel.
For more on Injustice 2, head here for an interview with Ed Boon about the next DC fighting game.