A lot has changed about the malleable story that drives the events of the Mortal Kombat series, but one of the touchstones of the franchise involves the hatred that kombatants Scorpion and Sub-Zero have for one another.  After all, each has murdered the another.  That sort of thing has a way of sticking in one's craw.  They are the last two characters in gaming that you'd ever expect to see fighting on the same, so of course that's just what developer Paradox Development decided to do with its thankfully canceled Mortal Kombat spin-off adventure Fire & Ice in which everyone's favorite palette-swapped ninjas joined forces for a co-operative title.  Game Informer has the details direct from Mortal Kombat creator Ed Boon:

"When they finished [Shaolin Monks], the guys at Paradox were gonna do another one called Fire & Ice. It was gonna be a co-operative Scorpion and Sub-Zero game," Boon said. "They actually started the early stages of that game, but they couldn’t do it in time and under budget, so the project was canceled and kind of went away."

He continued by poking fun at one of the less fondly-remembered Mortal Kombat titles. "There were a few that have been started, and some that never should have been finished. Special Forces probably shouldn’t have ever been shipped."

Let's be glad that someone came to their senses and canceled that project.  While I understand how attractive a notion it is to bring two of the franchise's most popular and recognizable characters together, their respective backstories make such a team-up narratively impossible.  Still, the idea of a co-op Mortal Kombat game isn't an altogether bad one.  The chosen pair just needs to make sense and be conducive to established characterization.  Why not Sonya Blade and Jackson Briggs working together on a special forces mission?  How about Cyrax and Sektor implementing assassination orders?  Maybe Baraka and Mileena flashing toothy grins at each other?  The alternative possibilities go on and on.