Today was the first time I ever got that bounty. If you get this bounty, just do the exclusion zone story mission up the difficulty so it's heroic. After dinkeldum hacks the machine and activates the fail safe, kill the yellow bar enemies. There's only 9 of them so leave a red guy to kill you. Since it's a darkness zone you have to do the entire thing again and get the 1 more Cabal major to finish the bounty.