While wearing each mask, you can – twice a day – teleport to locations where that monster can be found. Masks can also ensure that your next Slayer assignment is for its represented monster. This can only happen once a day for each mask, unless you are using a strykewyrm mask which has a three day cool down which is shared between the masks. Additionally, each mask also acts as a facemask.
Equip a Slayer mask and you’ll find its combat stats are optimised for victory over its related creature! Damage is boosted if you’re on a related Slayer assignment, extra Slayer XP is earned, and double drops occur for every tenth creature defeated – there’s even a useful counter displaying how many you’ve slain so far.
After a specified number of kills each mask will stop granting bonus XP, and stop providing extra damage and double drops. There are then two options: switch the mask to an awesome helm form (complete with emote) or use the Spirit of Battle[help]. Brand new to Treasure Hunter, the spirit of battle can be used to refresh a Slayer mask or helm and receive all its Slayer bonuses once more at the cost of losing your kill count.
What's more, open a chest this weekend and you’ll have double the chance of winning all ten previously released Slayer masks. And as if that wasn’t enough, all Slayer lamps and fallen stars (even prismatic lamps and stars used for Slayer) yield double XP during the promotional period!
For full details on Slayer masks, head on over to the wiki[help].