Up on the marketplace right now is the newest DLC for Mass Effect. Released just minutes ago it is called Pinnacle Station. It costs 400 points and lasts 2-3 hours. Again suprisingly Bioware haven't announced or spoken about this piece of DLC.
Update
To start the DLC you must have access to the galaxy map.
Pinnacle Space station was established for training the finest soldiers in Citadel space. Through the use of a combat simulator, soldiers are trained in four different ways.
Survival (like horde or l4d survival) pits the squad of three against unending waves of enemies.
Time trial involves Shepard hunting down enemies with his time being recorded.
There is a capture mode where points on the map must be captured with times being recorded.
And finally there is hunt mode, where Shepard has a set amount of time to kill enemies, but the time limit extends the more enemies he kills.
The DLC is combat based, but there are some light story elements. For completing all the training modules Shepard is put through one final mission (pretty epic) and then is very well rewarded.
Lasted about 2 hours for me.
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