First things first:
RAAM's Shadow DLC
is available for 1,200msp
) from the Xbox LIVE marketplace, or for free if you purchase(d) the Gears of War 3 Season Pass
This DLC is a lot of fun and let's you - for the first time - play as the Locust in the Campaign. To get this achievement you will simply need to select Campaign from the main menu, then scroll down to "RAAM's Shadow Arcade". Any difficulty will unlock this achievement and mutators are OK. If you play with a full group of 4 people you can also progress toward the following achievement:
Below is a list of the other achievements you can obtain during arcade mode, as well as a series of video walkthroughs from theRadBrad
if you ever get stuck. If you prefer, here is a written guide
. Have fun everyone!