Below is a video by iconoclast575 that I used for this beast of a trophy. Take the time, watch and learn - the guy/girl (person?) that made this video knows what they are doing.
Also, I have read in a few places that there is a glitch for Mission 19 - after you beat the first wolf, if you run off the right side of the map (and fall into oblivion) you will respawn and not take any damage throughout the rest of the mission. Being that I am not opposed to using in-game glitches, I gave it a shot, but was disappointed.
Questions, corrections and neg vote justifications below.