Board Thread:Mortal Kombat X/@comment-3513642-20150417213926/@comment-27004474-20150419080147

Dark Emperor Liu Kang is unlocked through the Tower Challenge. Not sure about what you have to do, but I played through the tower over and over and it eventually unlocked.

Hotshot Johnny Cage is unlocked by winning 10 matches in King of the Hill: Survivor.

And I unlocked Revenant Kitana through either playing online or playing KOTH.

Hope this helps.