i found the story mode intro to mk9 http://www.youtube.com/watch?v=-NsnAFZxgKE it takes place after armageddon thats all im gonna say i dont wan't to ruin the intro,go check it out.
After doing 300 challenges i dont think its worth it. Even tho i love Mileena.
I think if you did all 300 you should get every thing in the Krypt. Or at least more then one thing. I know its just not ...
Looking around on youtube i found the challenge tower "big reward" tell me what you guys think of it http://www.youtube.com/watch?v=OwNZWqNeOtw&feature=related