CapCom and Valve announced an additional DLC (downloadable content) for Resident Evil 6 (RE6), featuring the main protagonists of Left4Dead 2 (L4D2), Coach, Ellis, Nick, and Rochelle in RE6's 'The Mercenaries No Mercy mode'. Furthermore, Capcom (CC) has enabled the characters to use their own sets of abilities and weaponry based on the stories from L4D2. However, thats just where the fun begins, CC has also added villains i.e. The Witch and the Mini Tank. The DLC is aimed to be available April 5th.
Unfortunatly, you won't be able to play any Resident Evil Characters in Left 4 Dead 2, but again you can fight the main monsters, Lepotitsa, Napad, and Ogroman. According to Valve the DLC is schedules for 'Spring'.
These contents will only be available for the PC version of the two mentioned games and will be completely free of charge, downloadable as an update through Steam. Valve and Capcom hope to increase their sales and to awaken mutual intrests in their gaming audience.