Halfway there
Reach 50% completion in the normal mode or mercenary mode.
3/3/2011
11:59:08 PM
Very Rare 5.6%
...And Stay Down
Kill 25 crawling enemies with Stomp (single player only)
2/19/2011
11:03:17 PM
Rare 14.5%
The Sampler Platter
Kill a Necromorph with every Weapon in the game (single player only).
2/19/2011
10:11:02 PM
Very Rare 8.7%
C-Section
Knock down an enemy with Contact Beam Alt-Fire then kill it with Primary Fire before it stands up
2/9/2011
4:45:39 AM
Rare 11.3%
Clean Cut
Sever all three tentacles of a Lurker with one Line Gun Primary Fire shot (single player only)
2/9/2011
2:14:44 AM
Rare 21.7%