Capcom Unity has word that those who pre-purchase Resident Evil 6 on Steam (which are only underway for a few more hours) are now entitled to a free copy of the Onslaught DLC: "Onslaught DLC mode will also be available for those who pre-ordered the game on Steam. It can also be purchased separately for $3.99 or €3.99. as you can see from the video it plays like a single player mercs match except your opponent is playing on their own map and you can send your combo kills (shown as sort of moss covered baddies) over to the other players game to overwhelm them."