You will unlock/aquire the required items as followed:Grenadier Skill
Is unlocked automatically once you finished "The Forge" tomb. There is no skillpoint necessary to aquire it.Umbrage 3-80 Shade
Do not mistake it with the black version which you get right when you start the DLC. The ones required for the trophy has a RED
weapon skin and you will get is automatically once you've talked to Abby and Pilar in Kuwaq Yaku, your final objective (return to Pilar's house) after completing "The Forge" tomb.Brocken Shadow outfit
Also aquired after you have completed "The Forge" tomb and after you talked to Abby and Pilar in Kuwaq Yaku. The outfit is the one with the RED
boots not the black ones.
Once obtained everything simply go to the next campfire and equip all required items and exit the campfire and the trophy will unlock!