Once per day, while wearing the relevant mask, the next assignment the player receives will be abyssal demons. 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. This does not work if they are in the process of setting up a co-op Slayer assignment.
Twice per day, this mask will teleport you directly to a choice of locations where abyssal demons can be found.
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 experience 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, as a cosmetic preference only – this does not restore the Slayer experience and double drop effects to the mask.
A right-click option activates an emote in which the player is transformed into an abyssal demon for a few seconds.