Memento Malum

A Memento Malum is a weapon, typically a sword, created by the few Berserkers that have the patience to go about the process of creating a magic item. While most Berserkers go about on a rampage slaughtering indiscriminately, the refined smiths of the Memento will spare a child or two from the village they massacre and leave them with the weapon. When the Memento is dropped, it will always point in the direction of its creator. It will also subconsciously remind the victim of all the evil the demon has done to them and others, filling their soul with wrathful vengeance. Unless the weapon is disposed of, its user will be driven to avenge their lost loved ones.
The Berserker feeds on the rage of its victim and will become far more powerful if it slays the suffering soul. It is possible for the victim to successfully slay the demon, but such occurrences are rare due to the ungodly power they possess, coupled with the fact that the Memento often drives the user to act rashly and to fight the demon unprepared. Even if the victim does overcome the odds and slay the demon, the rage that burns within them and the release of Wrath energy can possibly convert them into a Berserker themselves. 
The best way to dispose of a Memento Malum is to bury it deep beneath the earth. It will continue to afflict its victims with visions of agony and whispers of vengeance until the magic fades from the item and the victims comes to terms with the events that transpired.