9dragons Wiki

A Mask is an item in 9Dragons that hides the user's Name, Hero Band, Level, Role, and Clan. They can be purchased in Hefei from the Unseen Scent NPC for 11,000 gold.
Masks have a duration of 30 minutes, but can be removed sooner by right-clicking the mask icon in the top left corner of the screen.
Masks can be forcibly removed if a player uses the Revealing Hand Maneuver.

While masked, clan guards will attack you. Also, if your mask is removed, you will be branded a criminal, and all players will be able to attack you for 5 minutes, regardless of clan.

While wearing a mask, your karma does not change. If you are killed while wearing a mask, you lose karma.
Killing a masked player will earn you karma.