NEW DLC. Offers co-op and much, much more!
I haven't played for a while so I've just re-downloaded the original game (reformatted PC since I last played it) and I'll see if I can get back into it. Apparently if someone who has the DLC (which gives you co-op and other new game modes) they can share it with you... I guess that means if they challenge you, you'll be able to play the new games? Not sure.
@Rummy :p