There is 1 Dead Ghosts to be found in The Buried City. They can be collected on any mission or during a patrol. Each Ghost can only be collected once per account.
Ghost 1[edit]
Head down the walkway. You want to look for this billboard:
Head over to the the walkway here. Climb onto this small ledge and jump from there onto the roof of the building with the billboard. This is for Offworld Transit (OWT).
Turn toward the middle of the billboard. Look around it to find the Dead Ghost
