Task Finder
...
From the Forbidden Lands Site of Grace, ride your way east towards the Grand Lift of Rold. There are two roaming bosses to encounter in the Forbidden Lands; the Night's Cavalry that spawns at nighttime and the Black Blade Kindred guarding the entrance to the lift.
The former is close to the Site of Grace, and he drops the Ash of War - Phantom Slash upon defeat. The Black Blade Kindred drops both of his weapons upon defeat. There is also a Phantom Tree with a Golden Seed underneath it near this boss fight.