Mortal Kombat X second kombat pack will include 4 new characters, 2 are guest characters and they are Leatherface from The Texas Chainsaw Massacre films, the Xenomorph from the Alien franchise, Bo Rai Cho who is a returning character and finally Tri-borg who is an amalgamation of three cyborg characters (Cyrax, Sexktor and Cyborg Smoke) from previous games.
There is no information yet on if it will include any other things such as costumes or new stages.
My own thoughts: I am glad they are supporting the game though I was unlucky enough to get the PC version and while it is better than it was at launch it still has plenty of issues. I noticed at the end of the trailer when the text saying “Mortal Kombat X available now” it showed the PS4 and Xbox One logo so i really hope it will be for the PC.