NOTE: MISSABLE!! Thanks to Ms Dudette for confirming you CAN obtain this if you miss it the first time, by joining someone else doing the quest!
You must have completed Chapter 5 of the Cloaked Ascendancy Campaign(last chapter) in order to start the new Shroud of Souls quest line.
Then, go talk to Sergeant Knox in Protector's Enclave and accept the new quest "The Dead and Defeated".
He'll ask you to meet him in the famous Driftwood Tavern.
Once in the Tavern, simply go upstairs to meet Knox and talk to him.
At some point before you leave, press
on the keg of ale on the table for this achievement.
There's a fun screen effect that happens when you take a drink!