The Mask of Broken Fingers provides several bonuses for players looking to train their Slayer skill. After killing 100 Crawling hands it becomes a Helm of the Dead Hand which has similar benefits, but does not provide double drops, extra damage, or an experience boost.
It is obtainable from Treasure Hunter and has no requirements to be worn. Although the mask is a free-to-play item, the bonus experience effect has no benefit. This is because Crawling hands require level 5 in slayer to kill and slayer experience is not gained over this level on free-to-play worlds.
Killing crawling hands while wearing this mask will grant additional Slayer XP equivalent to the Slayer level required to fight them (in this case, 5). This is given regardless of the current assignment the player has and in addition to assignment and/or contract xp. The XP awarded by the mask can be boosted by items.
Every creature killed is tallied, while the mask is worn. Each mask has a set amount of kills assigned to it that, once reached, "uses up" the Slayer XP and double drops effects, and turns the mask into a helm. The kill count continues to be tracked beyond this point, up to 999,999 kills.
A right-click option outputs total kills of that creature. If the helm has yet to be unlocked, there’s also a message to say how many more kills are needed to do so.
After the helm version has been unlocked, the player is free to switch between it and the mask version - only cosmetic effect – this does not restore the Slayer XP and double drop effects to the mask.