Me, my cousin, and nephew had an "idea" to try and help my slightly underpowered nephew through this. Our theory: run it with him up to the boss, get it low, then bail and let him finish the boss.
It goes well until the boss is basically one shot, and it hits me, I'M the leader. In the time it takes me to promote him (console)....YEP! The frames kill the boss before I can leave...
We did pull it off next try but no exotic reward. I'm 99.9% sure if this was a thing, someone would have spilled the beans by now. Anyway he's since leveled up and on the grind legit now.
I get "really sinister version of L from Death Note" vibes!