"The battle to save the galaxy rages on and a familiar foe returns in the largest downloadable content pack to-date for Mass Effect? 3 multiplayer! Available to download at no additional charge*, Mass Effect 3: Retaliation ups the challenge by adding treacherous environmental hazards to existing maps and will introduce the infamous Collectors as a new enemy faction in multiplayer.
Also making its way into the Mass Effect 3: Retaliation pack is a brand-new challenge system that will reward players for their accomplishments in multiplayer. This new feature will give players the ability to track and compare progress across different multiplayer challenges."
*You have until 9th October 2014 to claim the DLC for free.