Monster's dance
Have a guard incapacitate 3 civilians while he's poisoned.
7/7/2012
9:40:07 PM
Rare 19.3%
...And Stay Down
Kill 25 crawling enemies with Stomp (single player only)
7/3/2012
4:58:48 PM
Rare 14.5%
C-Section
Knock down an enemy with Contact Beam Alt-Fire then kill it with Primary Fire before it stands up
7/3/2012
12:15:05 PM
Rare 11.3%
Frozen in Time
Kill 50 Necromorphs while they are in Stasis (single player only)
6/30/2012
9:41:00 PM
Rare 28.0%