APPARENTLY this level wasn't brought to my attention until yesterday, just as the cutoff date for the achievement/unlock was ending. While I helped some friends get through it on Hard late last night for the unlock, I wanted to return to it and take on the twin Patriarch clones on my own.

Patriarch setup and fight:
https://www.youtube.com/watch?v=Az8.....uZnfc#t=19m53s

1st wave
https://www.youtube.com/watch?v=Az8.....1uZnfc#t=0m44s