In Mass Effect 3 for the PC, PS3, and Xbox 360, you can unlock the Quarian Engineer as a character to use in multiplayer, which is a fast and effective support character.
The Quarian Engineer is a rare card that you can unlock by purchasing any of the packs, however your chances are a lot better to get characters by purchasing Veteran and Spectre packs instead of Recruit packs.
Check out my other guide for more unlockable characters in Mass Effect 3 multiplayer.
