Blood Dragon 3 (Side Mission)
After completing Quiet on the Set, visit the region later for a call from Guy, begging for your help. Enter the now-accessible mine to reach him.
Speak with him again to start the mission.
You'll need to lure some Angels in- just head outside and get one to chase you. If you've already completely Dr. Charles Lindsey's missions, your bait will help as well.
Once you've lured one inside, others will start pouring in. You have a laundry list of murder methods to perform- the first three are killing with fire (molotovs count), killing with melee (fists and brass knuckles count), and three headshots (both bullets and arrows count).
After you've checked those boxes, you'll need an explosion kill, and a death-from-above, which you can get from the catwalks, or even the rock ledge by the stairs.
Fulfill all the required desecrations to complete the mission for a cash reward.