Warhammer 40,000: Boltgun

Just like the main game, the DLC campaign lets you use cheats without penalty, so to make this achievement super-easy (and my apologies if you want to do this the honest way, I have no advice for you other than be prepared to save often and die A LOT as enemies often spawn all around you and their attacks drain your shields/health in no time), go to accessibility in the options menu (from the start screen) and turn on invincibility and you literally cannot die from enemy attacks (they'll remove your shields but not your health). You CAN lose health by falling into pits (I don't know if it will kill you doing that if you fail enough times, and there are a couple tricky jumps, so if your health gets too low, I'd backtrack and grab health pickups, switching the run button from "hold to run" to "click to switch between running and walking" also helps as it makes it easier to avoid accidentally going out of run mode while you're lining up the jump). To make the achievement even easier/faster, turn on infinite ammo and all weapons unlocked and switch to the grav-cannon and just annihilate everything. Unlike most weapons, the grav-cannon doesn't even need to reload so you can just constantly fire a green beam of death which melts pretty much every enemy (apart from bosses) in a second or two and has an impressive splash damage AOE. There are also two new weapons (missile launcher/multi-melta) in the DLC which are also pretty powerful, but I found them less effective than the grav-cannon for just tearing through the levels. Also note that all difficulty achievements stack.