Killing spree + Blade Flurry = death to all
Step through the shadows from enemy to enemy within 10 yards, attacking an enemy every .5 secs with both weapons until 5 assaults are made. Can hit the same target multiple times. Cannot hit invisible or stealthed targets.
AND
Increases your attack speed by 20%. In addition, attacks strike an additional nearby opponent. Lasts 15 sec.

How do you combat against this? It murders your entire team within 5 seconds. Even better is when they pop cloak of shadows and then unable to TS off you.