From Guild Wars Wiki
The Mask of the Mo Zing can be obtained from Vael inside Grothmar Wardowns (right outside of Longeye's Ledge) for 250 Superb Charr Carvings.
- Note that Vael will appear as a collector only after you have done all of his quests. If any person in your party hasn't finished them he will appear as a quest giver near the center of the map
- Has armor rating and bonuses equivalent to normal headgear for the profession
- Can be upgraded by runes and insignias
- Can be dyed
- If you happen to have an Eyepatch, it will not clip through
- Gives <Item's Attribute + 1>
- Has clipping issues with earrings, such as the female paragon

Bug.
The mask sticks to your face, so if your character has a beard, it will clip through the mask.
[edit] Trivia
- According to Guild Wars lore, a Mo Zing is a masterless assassin. Zenmai is one such assassin.
- This mask bears a strong resemblance to some masks worn by ninjas in general fantasy lore.