Prodeus

Requierement:
Double Jump
Dash/Boost
Rocket Launcher (not necessary)


1. Start Sacrum Level (any difficult)
2. Walk to the first 2 Zombies and look over the cliff you can see the Bridge where the Elevator to the Yellow Key Card is. U need to Jump over the cliff to the Elevator side with a long double jump and long dash in other hands you die easy there.
3. In front of the Elevator there a two Imps, kill them, call the elevator, kill all Zombies on the elevator and jump quick on it to avoid damage from spawning Enemies (You can go slow and kill all safely or speedrun through).
4. Get the Yellow Key Card and be careful of the 3 Shotgunners on top stairs.
5.Run as fast as possible to the Red elevator straight ahead or Kill all safely with your Rockets. Be carefull of shooting Imps.

If you dont get the Achievement you habe taken some Damage. Try again!

Thanks!

Gidorra's method for the 'Sacrum' level worked perfectly for me when I unlocked this, but I also managed to do this again using the same route when going for the “Pacifist” achievement (on the easiest difficulty). As such, I thought I'd share this clip so you can see the enemy spawns and how to clear the gap at the beginning (If it seems like your double jump isn't working that means you didn't actually jump from the initial ledge and instead ran/fell from it. When that happens, one of your jumps is taken from you, thus making it impossible to clear the gap. You need to make sure that you are in fact jumping from that initial platform to make it across).

I clearly got lucky missing a fireball at the base of the elevator, as well as missing a zombie lunge while on the elevator itself though. To play it safe I'd recommend carefully/methodically killing all enemies until you get the red key card, then just sprinting through all incoming spawns straight to the exit.

So I managed it on the third level, “Fuel.” I replayed it on the easiest mode, using mostly the shotgun and the pistol.

It is a short-ish level, has a reasonable amount of enemies, no major ambushes, lots of corners to lure enemies around, and only a couple of trouble spots. I did two quick runthroughs to memorize the layout, and then made one final run for the achievement.

As long as you’re careful with the handful of fireball enemies and the occasional shotgunner, there’s only a couple of tricky areas. One early area has a couple of shotgunners and a handful of the zombie-like enemies. On my first trial run, I got pegged by one of the shotgunners. On my successful run, I waited at a corner for the enemies to come to me.

About midway through, there’s a passage where enemies spawn after you hit a button, three fire ballers on each side. You can either favor one side of the room out of range of one batch while you take them out, or there’s a button you can shoot that triggers a trap that kills all of them.

The other problem area is where you exit a hallway and there’s a upwards slope on the right with enemies descending along with exploding barrels. Shotgunners are among them. Trying to blow up the barrels before they reach the bottom is tricky, as they’re mixed in with enemies and have a decent blast radius. Plus, this leaves you vulnerable to the shotgunners. I managed it by running around the corner to start things rolling (no pun intended), backing up to a distance into the hallway to where the slope/entrance was barely visible, and then waiting for enemies to emerge as they reached the bottom. It’s a choke point, so just gun them down.

The final possible trip-up is at the exit. There’s a shotgunner guarding the rail car where the level exit is located...the same rail car that you start the level in. He can get a lucky shot off as you’re mopping up the enemies leading to the exit point. If you favor the left side of the map, he usually can’t get sight of you while you finish everything else off. After that, take him out with a well-place pistol shot at a distance or shotgun close up.

Good luck! If this solution is not helpful, please let me know rather than just downvoting it, so I can alter it as needed.

I earned this on my first try on the Memoriam level. Their are only 45 enemies in a wide open area and no enemies spawn until you hit the switch out in the middle end allowing you to max out your ammo. After hitting the switch you must quickly jump up to the armor on your left and up to the rock area beyond it, double jump is required. You can hide behind the rock pillar here and take your time, enemies will spawn slowly as you pick them off, although to get them to spawn you may have to walk out to your right along the memorial, quickly heading back behind the pillar as they spawn.

Besides the usual fireball throwing and flying enemies you'll need to watch out for a shotgunner who stays in the middle, I kept taking a quick shot at him and then ducking back behind the rocks, also the sniper who will appear above the starting area after the halfway point. The rest of the enemies including some shotgunners will pile up along the memorial beneath you and it's easiest to bounce grenades down there to wipe them out.

Best to play this on Ultra Easy as enemies die with less hits and shoot less often.