Assassin's Blade

Assassin's Blade is a one handed dagger with good bonuses to Agility and Critical Strike.

Source
The dagger is a random drop from mobs in Shadowfang Keep.

In the RPG
Intended for use by Horde assassins, these charcoal-black daggers are designed for striking directly into the hearts of foes. Even when held up to the light, they do not glint or produce any sort of reflection that will give their wielder away. Its powers only work in the hands of a Horde assassin.

Trivia

 * Assassin's Blade appears as a basic weapon for the Rogue class in Hearthstone. The flavor text reads: "Guaranteed to have been owned by a real assassin. Certificate of authenticity included."