There is an imbued version of this item here.
Black masks are helmets worn in the head slot. The mask has the same stats as a black med helm. It gives a player 15% Attack and Strength boosts against all monsters on the player's current Slayer task. You need 20 Strength, 10 Defence and 40 Combat to wear it.
The Black Mask is a rare drop from Cave Horrors which many people camp as black masks are high in demand. However killing them requires 58 slayer and many quests must be done, which deters many players from killing them.
When dropped by Cave Horrors, the mask has 10 charges that will be discharged to monsters at random. Each one of these charges reduce's the opponent's Defence by 3-10 levels. Once the mask has been drained of all 10 charges, there is no way to recharge it; although the Attack and Strength boosts still remain.
For 1,250,000 nightmare zone points you can upgrade your black mask to a Black Mask (i). A Black mask with charges (1-10) can be imbued.