When the last Mortal Kombat came out, fans got some real treats in the form of guest characters. The first was the Elm Street Slasher himself, Freddy Krueger. The Dream Master fit in nicely with the world of Mortal Kombat and more than held his own. The second was God of War's Kratos, also a worthy kombatant.
Ed Boon has already revealed that guest characters will return in the newest game, and because of that, speculation is completely rampant. I delved into some of the possibilities, and these five are the ones I think are probably the most likely.
Fulgore I freely admit I bought Boon's April Fools' Day joke of a confirmed Mortal Kombat / Killer Instinct crossover. Such a union has been rumored for years, but it seems no closer to happening than it ever was.
However, that was all before Microsoft brought KI back as an Xbox exclusive. Much as they did with Kratos last game, it would probably be an easy sell to Microsoft to offer the main mascot of Killer Instinct as a bonus fighter to give them the edge over Sony. He would fit in nicely as a prototype of the Lin Kuei cybernetics project, and works well in the brutal new world.
Plus, who doesn't want to see NetherRealm render that ridiculous machine gun-head fatality with all their gory skill?
And on the PlayStation side...
Sweet Tooth Boon himself retweeted suggestions of Twisted Metal's clownish killer, but Boon is also known for trolling fans. Nonetheless, Sweet Tooth would make for a very compelling PlayStation exclusive. He's a ruthless murderer who lives only for the thrill of the kill, and his inclusion is easily explained as either the result of a Twisted Metal contest winner's wish or perhaps even as part of the delusions that the games sometimes take place in.
Mad Max Rockatansky For everyone who is hoping for Jason Voorhees or Pinhead or another horror icon like Krueger, you guys are probably going to give up that dream. Krueger made it into the last game because Warner Bros. had just distributed a rebooted Nightmare on Elm Street, something that is easy to see in the fact that it's clearly Haley's Krueger, not Englund's.
But you know what is coming out very soon, both as a movie and with a tie-in video game from Warner Bros.? The one and only Mad Max! Tough, skilled in pit fighting, and heavily armed, Max would pair nicely with the Master Blaster homage, Ferra / Torr. No idea how the hell Max gets into the fray, but he's the absolute closest parallel to the addition of Krueger in 2011.
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Harley Quinn Warner Bros. also has the DC Universe to play with, and that includes the award-winning Arkham games. The most obvious choice is Joker, but the fact that Shang Tsung used a generic clown for his hidden fatality mimicking Joker's fatality from MK vs. DCU shows that the franchise might be reticent or unable to include the Ace of Knaves.
That does leave Harley Quinn open for use, though. Quinn is supposed to appear in Warner Bros.' upcoming Suicide Squad film, and she's already an established part of the Arkham games' so she fits nicely into multiple categories. Her Suicide Squad actress, Margo Robbie, is probably outside NetherRealm's budget for voice work, but they could always work with Tara Strong. Plus, the fighter series always needs more women. The banter between her and Cassie Cage alone would be worth the price of the DLC.
The Undertaker It's kind of flown under the radar, but Warner Bros. and NetherRealm are teaming with the WWE for a mobile game called WWE Immortals. It's designed to take the WWE roster and make it larger and more mythological, taking the term "Hell in a Cell" a bit more literally than it usually appears.
It would be a criminal waste of the opportunity to bring in a member of the WWE roster as a guest character. That said, the number of wrestlers who are good fits for the series and almost guaranteed to finish their careers in the WWE is pretty small. Nobody in their right mind would risk rendering Brock Lesnar for a game with his history, but The Undertaker? He's going to be in WWE until the very end.
Considering how much of Mortal Kombat X seems to focus on the dead and necromancy, it only makes sense for The Phenom to come claim his domain from someone like Quan Chi. If you want to know what that would look like, go pick up those trade paperback collections of the Chaos comics he starred in. That version of the Dead Man just begs to be dropped into a video game.
We'll find out if I'm right soon enough, but for my money, one or more of these five is on their way to test their might.