This trophy will drop from completing a regular 820 Nightfall or Nightfall:The Ordeal strike from the Forsaken DLC.
Strikes to look out for, Warden of Nothing (Tangled Shore)
Broodhold (Tangled Shore)
The Hollowed Lair (Tangled Shore)
The Corrupted (Dreaming City)
It is easiest to complete on Nightfall: The Ordeal at the Adept difficulty, its basically a regular strike with matchmaking
Dont panic IF you have yet to get the trophy, The Dreaming City AND Tangled Shore are NOT being Vaulted in November when the new DLC arrives