The Helm of Darkness is a helm that provides several bonuses for players looking to train their Slayer skill. It is obtainable by killing 1000 Dark beasts with a Mask of Gloom, which can be won on Treasure Hunter. Unlike the mask, this does not provide double drops, extra damage or an XP boost, but does give access to an emote. The helm must be worn in order to perform the emote which can be accessed by right clicking the mask and selecting "Transform".
Once per day, while wearing the relevant mask, the next assignment the player receives will be dark beasts. They will still need to go to a Slayer Master that normally assigns these creatures – if they do not, the player will be told which Slayer Master assigns them, and then receive a random task as normal. This does not work if they are in the process of setting up a co-op slayer assignment, or when the slayer master is offering a special challenge.
Twice per day, this mask will teleport you directly to a choice of locations where dark beasts can be found.
A right-click "check kills" option announces total kills of that creature. The announcement of total kills is not seen in the chat interface but is seen above your character by those around you.
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 1,048,575 on the item's tooltip. However, only up to 999,999 can be displayed to others with the "check kills" option.
The player is free to switch back to the mask version, as a cosmetic preference only – this does not restore the Slayer XP and double drop effects to the mask.
After the helm version has been unlocked, the player also unlocks an emote in which they can transform into a dark beast for few seconds.