Unlocking Prophecy weapons (Curse Of Osiris DLC)
To unlock Prophecy weapons in the DLC, you must first complete the story and all three Mercury adventures, then return to Brother Vance to get a Legendary engram, which allows you to unlock the Heroic version of the three adventures. Once you beat one of the missions on heroic, you'll get the "Lost Prophet, Verse 1" reward from Vance. Activate it with multiple Radiolarian Cultures obtained from Public Events and other chests, then return to Brother Vance to forge the Prophecy weapon.
Perfect Paradox legendary shotgun (Curse Of Osiris DLC)
Successfully complete the Lost Prophet Verse quests given by Brother Vance at the Lighthouse on Mercury until you are given the "Lost Prophecy, Another Verse" quest. Complete that quest to unlock the Perfect Paradox legendary shotgun and The
Legend Of Saint-14 emblem
Sagira's exotic ghost shell ("Curse Of Osiris" DLC)
Complete all 11 Lost Prophet Verse quests given by Brother Vance at the Lighthouse on Mercury to get Sagira's exotic ghost shell and the "Prophetic Arsenal" emblem.