Armored Core VI Walkthrough - NG Ch1 M8 "Operation Wallclimber" S-Rank

Do the training before you do this mission, you get some decent parts, two of which I've used in the build for this video.
Boost left-ish over the mountain and first canyon/wall . Go straight to the wall and take out the artillery. It's worth something like 10 seconds per hit of S-Rank time (less ammo/damage). Go back to the middle and take out the big guns near the Tetrapod so they don't mess with your fight. Once the four-legger is down hit the gatling cannons located back along the main road, then boost back to your little hole in the wall. Take out mooks on the way through the wall if you can do it without slowing down. Do no slow down. Resupply.
The boss fight is a bit of a trick because it basically doesn't take damage from the front. Let Rusty be the target while you hit the booster block from above/behind. In phase 2 Rusty gets totally legitimately called away, and you have to do both roles yourself. Lucky the movements of the boss don't change much apart from dropping mines.