☠️ You can't complete The Emissary quest until much later in the game.
☠️ You need the Shield Transmutation which you get at the university to pass through the poison clouds.
☠️ This is the final transmutation you unlock and it's impossible to miss.
The Emissary quest in Valor Mortis is likely the next you'll encounter after crossing the bridge in the Valley of Ashes and making your way into the army camp.
You'll find the seal of an emissary from Bonaparte in an abandoned carriage, but the quest will indicate you somehow need to get through the clouds of poison infesting the camp to progress it further.
To do this, you need the Shield Transmutation ability, but you won't unlock this until much later in the game, when you visit the university in the city. The Valley of Ashes is the game's 2nd area, while the university is the 9th, which puts into perspective just how much you'll have to first progress in order to return and complete this quest.
Once you do have the ability, use it to cross the poison, head through the camp, and interact with the unusual corpse to start a miniboss fight of sorts. After this, open the chest to get the Perfect Copy amber, which increases the ranks of all other equipped Tier 1 and Tier 2 ambers.
