Although it's already been confirmed that Injustice 2 is slated to receive a character from the Mortal Kombat universe with Sub-Zero coming as DLC, the developers at NetherRealm Studio have also buried a reference to the brutal fighting game in the title, by hiding a fun little Easter egg mentioning a trope from the gore-soaked series. Those looking for the secret trinket can find it while playing in the DC Comics-inspired brawler's Gotham stage.
As seen in the image below from the Redditor known as AlkalinePacino, when fighting on Injustice 2's Gotham stage, it's possible to change the theater marquee's message, which originally displays two fake movie titles on either side under the names Final Wish 2 and Hidden Crimes, to read "Finish Him," which is the Mortal Kombat series' iconic phrase that sets up an often grisly finishing move. In order to do so, all fans have to do is slam an opponent into the marquee three times to have the letters fall off to show the Easter egg.
In addition to the aforementioned nods to NetherRealm Studios' original fighting game franchise, there's also a more obscure Easter egg dedicated to Mortal Kombat's Cyrax that can be caught while playing though Injustice 2's story campaign, so those who don't want to encounter spoilers of any kind would do well to jump directly to the next paragraph. During a cutscene, Catwoman and Cyborg are about to get blasted to bits by a mainframe computer, when all of a sudden, Selina Kyle spouts out an override call sign to stop the system "LK-4D4," which happens to be Cyrax's code name.
Taking all of this into consideration, it's highly likely these are just a handful of many Injustice 2 Easter eggs dedicated to Mortal Kombat. Since the DC Comics fighting game has only been out for less than a week, it's quite possible that plenty more will be discovered in due time.
Injustice 2 is out now for PlayStation 4 and Xbox One.