shao kahn master of the lower mines skin .... it's unobtainable at the moment, along with a bunch of others , according this reddit thread here :
https://www.reddit.com/r/MortalKombat/comments/by3yoa
since we had the Kronika gold vault that gave us the "unobtainable" jax Steel Patriot skin, you can expect the same method for this shao kahn skin, will come up suddenly in future, in the same way, through a special golden globe , accessible for only 24 hours inside the krypt ....