You'll run into multiple Angels throughout the game. Easiest way to do this is as follows: First upgrade your Frag Thrower, you don't have to all the way, but it makes it a lot easier. Also I had reflex booster upgraded as well. Again not needed but makes it incredibly easy. Remember you can respec your points at any time, so no need to worry where you put them for this! After depleting their health bar they will spew out 3 canisters at a time to be destroyed. There are like 12 or so total (you'll see an image showing how many are left.) Once the Angel has just one canister left, whittle his life down and make sure your up in his face! Once you knock him out, he'll start to retract to shoot out the last canister. At this moment start your slo-mo (Press Right Thumbstick In,) then spam the frag thrower ( Mash X.). At this point as he launches the last canister, if done correctly your explosion will take it out as well as him at the same time. Cheevo will pop instantly! Hope this helps!
Let me know if anything isn't clear! Thanks guys! Hope your enjoying this game as much as I am!! GO GET 'EM PUPPY!!