Assassin...

The Assassin walks the shadows, a deadly viper ready to strike at the heart when an enemy least expects it. Assassins are masters of their chosen weapon, the dagger, and are experts at inflicting Critical Strikes that cause massive damage. The Assassin is trained to efficiently link attacks together in a chain without giving an enemy a chance to hit back. Wearing only lightweight armor, they have mastered the ability to move as shadows, avoiding damage by not being there when an enemy's strike lands. Their other magical skills include Hexes that lower a target's defenses and protect the Assassin from harm.
Assassin Attributes
Critical Strikes
(Primary) For each point spent on this primary attribute, the Assassin gains an additional 1% chance to score a critical hit. Assassins can also gain Energy whenever they score a critical hit in this way.
Dagger Mastery Boost the Dagger Mastery attribute to boost the damage the Assassin inflicts with daggers and the chance to land a critical hit with a dagger. Many skills, especially dagger attack skills, become more effective with increased Dagger Mastery. This attribute also improves your chance of performing a Double Attack and striking with both daggers at once.
Deadly Arts Increase the Deadly Arts attribute to improve the duration and effectiveness of Hexes and other skills that make a single enemy vulnerable to the Assassin's strikes.
Shadow Arts Put points into the Shadow Arts attribute to improve skills that boost the Assassin's defenses and allow instantaneous shadow movement. http://www.guildwars.com/gameplay/professions/assassin/