User blog comment:Musicgirl14/How do I get DLC from MK9?/@comment-2195697-20110919062304

While ingame, you can check online for new features. Alternatively, you can go to the PlayStation Network Market and do a search for "Mortal Kombat"

I'd recommend the DLC Bundle Pack with all four characters. Also, you are going to want to download the Kombatability Packs in order to play online with said DLC characters. If you feel like it, pick up the Klassic Kostumes pack as well.