In Retaliation, a new multiplayer DLC for Mass Effect 3, the Collectors have returned and are available as a new enemy in multiplayer matches. You must prepare to face off against the Collector Praetorian, Scion, Abomination, Trooper, and Captain. Reports have also come in that Cerberus has enlisted the Dragoon to their ranks and the Geth are deploying new Drones to the battlefield.
A host of new characters have joined the war to fight this new threat, including the Turian Havoc Soldier, Turian Ghost Infiltrator, with many more being added on a regular basis. You will wage war across six maps, featuring new environmental hazards and traps. A regular rotation of Firebases will be introduced to different hazards as they come under attack. And you must survive the onslaught of Acid, Lightening, Meltdowns, Sandstorms, Swarms and Whiteouts. The Collectors have also brought deadly new weapons to the fight: the Collector Assault Rifle, Sub-Machine Gun, and Sniper Rifle.
Mass Effect 3: Retaliation is now available for free on October 9th, 2012, for PC, Xbox 360 and PS3.