The Heart of Ahriman should do instakill when it is slung and hits a monster with a head who is not wearing a hard helmet. To encourage this, Barbarians should get Basic skill in sling.

To compensate for inevitable cheap deaths, any monsters that are too important to cheaply instakill via this method need to be given hard helms of some sort.

The Heart of Ahriman should provide extrinsic protection like a ring of protection or one of the other quest artifacts that provides protection.

An artifact often gifted to Barbarians which provides magic resistance and half spell damage but prevents Pw from regenerating. Or assign these properties to the Heart of Ahriman, which makes it good for Barbarians as they rarely cast spells.

The Heart of Ahriman grants half physical damage, and Thoth Amon is nearly guaranteed to pick it up.