Gameitall 
Bioware had finally put a rumor to rest, giving us a new information that the Online pass that come with new copies of Mass Effect 3 is for a Co-op mode called “Galaxy at War.” The new 4-player co-op missions take place outside of the single-player game, and aren’t affected by your Mass Effect 1 or 2 saves. “Players can choose from a variety of classes and races, form an elite Special Forces squad, and combine their weapons, powers and abilities to devastating effect as they fight together to liberate key territories from enemy control.”
From information given though the trailer on the Xbox Live Marketplace, you can pick from all the classes you can select for Shepard, however, for the first time, your able to choose your race, ranging from Salarians, Asari, Human, and others. The multiplayer does tie into your single-player game in unspecified ways, offering “an alternative method” of achieving success in the main storyline.
The Multiplayer aspect seems to be a rather mysterious, and optional, system that uses multiple factors to augment Shepard’s “Galactic Readiness” level. “Other platforms and interfaces will be announced in the coming months,” BioWare said, also noting that it will be possible to obtain the “optimal” ending without doing anything in the Galaxy at War mode.
