Buy RS3 Black mask
The RS3 Black mask is a members-only head slot item made from a cave horror mask. When worn on a Slayer task, it gives 12.5% more Melee accuracy and 7.5% more Melee damage against the monsters in that task. This makes Slayer training faster and easier.
The mask needs 10 Defence, 20 Strength, and 40 Combat to wear. It is tier 10 tank armour with 40 armour and 100 life points. It also comes with ten charges. A charge can trigger at random when starting a fight and lowers the enemy's Defence level by 3 to 10. The mask keeps its accuracy and damage bonuses even after the charges run out.
The Black mask is a key part of the slayer helmet. Players who finish the Smoking Kills quest and learn the skill from a Slayer Master can combine the mask with other Slayer items to craft one. The slayer helmet keeps the mask's full accuracy and damage bonuses.
Black masks drop from cave horrors and unspeakable horrors in the Mos Le'Harmless Caves, which need level 58 Slayer to fight. The drops are very rare, so buying one skips a long grind.