Pirated versions do not receive official patches, meaning you will likely encounter game-breaking bugs that have already been fixed in the retail version.
Often goes on sale for under $10. Buying it here ensures you have access to the Mercenaries mode, online co-op, and cloud saves.
At specific points in the story, four players from different campaigns can meet up to fight a common boss.
You can play as a monster and "invade" other players' games to stop them from progressing.
Resident Evil 6 relies on Steam or Console Networks (PSN/Xbox Live) for its cooperative play and "Agent Hunt" modes. Pirated copies are generally blocked from these official servers, making stable multiplayer nearly impossible. Official Ways to Play Resident Evil 6