Capcom and Valve are working together to bring thwe world of Left 4 Dead 2 into the PC version of Resident Evil 6 and vice versa. A sort of crossover if you will. Oh, and it’s completely free.
Resident Evil 6 PC exclusive “No Mercy” mode will feature the cast of the beloved co-op zombie shooter as playable characters, each with it’s own customized weapons created especially for the game. Two of the iconic Special Infected zombies – The Witch and Mini Tank – will also appear in RE6 as random enemies, regardless of whether you play as  a character from Left 4 Dead 2 or Resident Evil 6.
The Lepotitsa, Napad and Ogroman – “some of Resident Evil 6’s most fearsome enemies”- will then cross over from the RE universe and into the PC version Left 4 Dead 2 for players to fight against.
Below you’ll find a video in which RE6 producer Yoshiaki Hirabayashi explains a bit about the coming crossover. Right after that there’s a messive amount of preview secreenshots.