Mutant Year Zero: Road to Eden

This is the first achievement you'll unlock in the DLC (story based anyway) - after travelling to the newly unlocked Mausoleum of Surburbia (sounds like a happy place) you'll get introduced to the newly added 'pod' enemies and their mutogens - after dealing with a fair few of them, you'll find the elder being harrassed by 4 of them in this area. After some friendly zone style introductions, you'll approach the elder and start a cutscene whilst also unlocking the achievement :)

on a side note, as of writing, i'm in the next unlocked area and both times cut scenes are meant to play, it kicks me to the dashboard and reloads after it's played - it's real annoying and i hope it doesn't become a trend