The dragon knife is a members-only ranged weapon and is the most powerful type of throwing knife available. It is obtained as a drop from wyrms, drakes, and hydras.
To wield a dragon knife, the player must have at least 60 Ranged. They can be poisoned and, as they are one-handed, can be wielded with a shield or god book for protection.
A player performs the dragon knife's special attack, Duality.
The dragon knife has a special attack, Duality, which consumes 25% of the player's special attack energy. It causes the player to throw two dragon knives at once, with each knife having their own accuracy and damage rolls.
This special attack is similar to dragon dagger's, albeit without an extra increase in accuracy and damage.
All monsters drop the dragon knife at a rate of 1/2,000 if killed as part of a Slayer task.
For an exhaustive list of all known sources for this item, see here