![](http://images.eurogamer.net/2013/articles/1/6/0/2/3/8/2/137512194941.jpg/EG11/resize/405x-1)
As detailed by VG24/7, Discovery is the most major addition as it's a story-based mini-campaign that teaches players the ropes of co-op. It's available for up to four players.
Once players acclimate to that, there's Unleashed mode, which tasks players with working together to guard chests, eliminate disguised foes, pull off synchronised kills, and kill "infected" enemies that can only be harmed once you've retrieved a package.
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