Exiles Blade

Exile’s Blade

Weapon (dagger), legendary (requires attunement)

The blade of this dagger is made of three metals: silver, adamantine, and cold iron. The hilt is engraved with Sylvan runes that speak of the transition between summer and winter.

Attuning to this blade requires swearing an oath to kill the current queen of a fey court. While wielding this dagger, you gain a +3 bonus to attack and damage rolls. Attacks with this dagger against fey creatures ignore any resistances or immunities to damage. Once per turn, when you hit a fey queen with this weapon, the target must succeed on a DC 21 Constitution saving throw or drop to 0 hit points. If you stab this blade into the corpse of a deceased fey queen, the blade and the queen both disintegrate into dust. The fey queen can’t be resurrected by anything short of deific intervention.

Ref: T&H p280