Cement his Torment is an achievement that requires the player to defeat a tormented wraith which requires the use of Jennica's ring and a set of black equipment consisting of an item to fill the head, torso, legs, main hand, and off-hand equipment slots.
Only black equipment will damage the Wraith. Elite black armour set and Black Knight captain's armour will work as well.
Head to the centre of the Dark Warriors' Fortress near 15 Wilderness. Once in the centre of the fortress near the hanging skeleton, use the "operate" function on Jennica's ring to enter the Spirit Realm.