The Skeletal horror is a monster which may be fought after completing the Rag and Bone Man and Fur 'n' Seek wish list miniquests. The horror may be killed once a week after completion of the miniquests, resetting every Wednesday at 00:00 UTC.
Once defeated, the Odd Old Man will thank the player and reward them for their efforts. The first time the creature is defeated, the player will be rewarded with 10,000 Slayerexperience and 7,000 Prayer experience. Subsequent kills will reward experience based on the player's Slayer level.
To fight the Skeletal Horror again the player must speak with the Odd Old Man and ask him to rebuild the creature; he will then rebuild the creature every week for the player to fight. Every subsequent fight after will reward the player with Slayer and Prayer experience based on the level of the respective skill.
In the old diary, it is suggested that the Skeletal horror's skull was the model for the black mask.
The Skeletal Horror is supposed to be an ancient beast yet most of its bones are from other creatures. Some, such as the skull, are presumably the original bones of the ancient beast that the Odd Old Man found.
The Skeletal horror has one of the 'non-chafing manacles' that was on the Odd Old Man's wishlist after completing the Rag and Bone Man quest and the first wishlist. It appears that the Golden Fleece is what makes it non-chafing.