The achievement “Friend of a Friend” is bugged. It says you have to play 16 different buddies in the BG mode. However, no matter how many buddies you play – either with the E.TC. Bandmanager hero or with other heros – the achievement does not progress.
The issue is solved after patch 26.4 
I confirm it didn’t work for me 2 times :(((
still doesn’t work BLIZZZZARD!!!
Please fix this Blizzard. I have 99% completion for the battlegrounds game mode, missing only this bugged achievement, and you know how frustrating that is 
Also bring back Chronormu!
new patch, still not fixed. Why?
still not working – plz fix!
After patch 26.4 the bug is gone. Now you can play 16 different buddies with the hero E.T.C. (doesn’t have to be in the same game) to get the achievement