Among the characters available in the last Mortal Kombat game was Freddy Krueger, the Nightmare on Elm Street character who was released as a downloadable add-on. A "guest" character like that is likely to also end up in the latest game in the series, Mortal Kombat X, according to series creator Ed Boon, although he isn't saying whom it might be just yet.
Speaking on a Mad Catz stream (via Event Hubs) at fighting game tournament Evo 2014 this past weekend, Boon revealed that Freddy Krueger was the most-downloaded character in Mortal Kombat. Likewise, Mortal Kombat's Scorpion was the most-downloaded character in Injustice: Gods Among Us, which was also developed by Mortal Kombat maker NetherRealm Studios. "I think there's a novelty to having a downloaded guest character," he said when asked about such a character ending up in Mortal Kombat X. "So I think the chances are pretty high. I don't think every single one of them will be a guest, but I think the chances of at least one of them will be pretty good."
Boon reiterated this in an interview with Polygon, saying of the strong Krueger and Scorpion downloads, "It's working out for us, and I'd be surprised if we ignored those numbers."
As for who this guest could be, a DC Comics character isn't likely--and not necessarily because of the reason you might assume (DC taking issue with such a violent game). "I'd be hard-pressed to have a DC character as a downloadable character in Mortal Kombat X," Boon told Polygon. "The main reason is, I have no desire to cut Batman's head off. I have no desire to kill Superman."
Even when you rule out comic book characters, there are still countless possibilities for who might end up in Mortal Kombat X. Horror movie characters like Krueger make for a natural fit because of the level of violence they'll be involved with--the improved visuals make Mortal Kombat X look especially brutal--but they aren't the only candidates. Don't forget, the PlayStation 3 version of Mortal Kombat featured Kratos from the God of War series.