The witchwood icon is a slayer equipment piece that is used to protect the player against the effects of the screams of cave horrors. It is going to be crucial if you want to survive these monsters.  You can buy the Witchwood icon from slayer masters for 900 coins. The amulet can not be traded with other players or bought from the grand exchange. You need a slayer level of 35 to equip it. This is kind of strange as it is only usable against the cave horrors who have a 58 slayer requirement.  If you do not wear this, the cave horrors can hit the player very accurately for 10% of their total hitpoints.