The Skeletal Horror is a boss monster you made receive when getting a boss task from a slayer master. It yields 106,000 Experience per kill and is one of the more simple bosses to deal with.
Fighting the Skeletal Horror
Fighting the skeletal horror is very simple. At the time of this writing all you need is a melee weapon (Whip or better) and basic defensive gear (Full rune, Dragon defender etc.) The rest of your inventory can be 3-4 Super Strength or Super Combat potions and Prayer Potions / Super Restores. (Note: This is if you have already unlocked the prayer Soul Split)
Simply enter the instanced area through the bone door, Turn on soul split and melee him. Periodically throughout the fight he will "break" pieces of himself off and you will have to click on them as they run along the ground. Failing to click on the pieces will cause the Skeletal Horror to rapidly heal 20 hp.
