So being bored I spent some gold on this to try it out myself. I'm not sure I grasp the mechanic exactly..
I try MFD'ing a minion and take him down, so in theory everything around him gets the big boom when the final blow comes, right? I have a feeling this doesnt work against the main elite in a pack? or maybe that damage isnt high enough (I'm doing WR MP8 for my testing).