RuneScape Classic Wiki

Not to be confused with a black dagger.

The main RuneScape Wiki has an article on: Dark Dagger
The Old School RuneScape Wiki also has an article on Dark Dagger.

The Dark Dagger is a quest item obtained in the Legend's Quest from Echned Zekin, a disguise of the demon Nezikchened. It may either be given to Ungadulu to receive a Holy Force Spell, or used to kill the spirit Viyeldi which converts the dagger into a Glowing Dark Dagger. It may be equipped in the weapon slot.