Id say try using something besides Nightstalker. I've been maining nightstalker since it was released and yesterday I played on my voidwalker and realized how much easier it was to use than the nightstalker class! Nightstalkers in general were never designed for pvp in mind and they are extremely weak compared to Titans and Warlocks. Even with shadestep, it's only situational and the entire class puts you at a disadvantage. Try bladedancer or gunslinger first, both of these subclasses have offensive supers and lots of ways to kill the opponent. Tripmines, skip grenades, throwing knives, etc...