Warner Bros. have announced that Jason Voorhees, the protagonist/villain of Friday the 13th horror movies will be added tomorrow to the cast of fighters for Mortal Kombat X, but only for those who own the Kombat Pack. If you only want to buy the character or Horror Pack, you may do so from May 12.
In addition to Jason Voorhees, the Horror Pack also includes alternative skins for Mileena, Reptile, and Ermac. You can buy the character, the skins, a pack with both, or the full Kombat Pack (which is effectively the Season Pass for Mortal Kombat X).