Starved mask of Amascut was removed from RuneScape after an update, but still exists in-game for those who had obtained it.
The Starved mask of Amascut was a rare, limited-time Squeal of Fortune prize that required 15 Defence to wear. It was available between 8 November and 18 November2013. Occasionally after killing something while wearing the mask, a delicious soul would appear, which could be clicked on to gain Slayer experience equal to 40% of what you would get from a small XP lamp. This could be done 20 times before the mask's charges were used up and it would revert to the Mask of Amascut, which is a purely cosmetic version of the mask.