Quake

PC cc solution
start new game on quake
~
Skill 3 (for nightmare mode)
map e1m1
god
noclip
don't shoot anything, find the stage end. (you're looking for a red light door)

You can use the axe, and pretty much have to as the last batch of enemies near the exit portal is impossible to run through.

I recommend jumping off the bridge near the beginning and taking a detour through the tunnels around the back, that way you can pick up +100 health and some armor so you can tank a few hits along the way, it's easy to run through the enemies up until the 3-switch part while going down the ramp with the acid pit, there you should start chopping up enemies as fast as you can. Once you reach the bottom door, it's pretty straightforward, bait enemies from around the corner, slice them with the axe and rush the exit.

Last but not least, try dividing the level into smaller segments and save after each one if you think you made it through an encounter with minimal health losses.

Easy if playing on PC.

Press tilde and type god once you load into e1m1.

Run through the level and let the enemies shoot each other if they block your path.

There are plenty of videos and guides online as to how to access Nightmare. You should be able to use level select to select the level and difficulty, otherwise you can use the in game route to get here.
But to summarise. The room with the gate to episode four has a wooden structure. As you pass through the pool close to the pool's edge you may be able to make out a part of the wood where you can land while keeping yourself moving in that direction. After landing walk along the wood to a space in the stone, this will lead you to a portal setting the difficulty to Nightmare. If you miss landing on the wood there is a portal that will take you back to the entrance of episode selection.

Fortunately you can make use of saving and loading as much as you want, as well as using the Axe to kill enemies.

I recommend working your way slowly through the level dealing with all enemies for the most part, dragging them around corners so you can axe them one by one, but you can go fast and strafe while using enemies for cover from enemy fire behind them and sometimes causing infighting, particularly between soldiers and dogs. Also familiarity with the level will help but is not essential as you can save whenever you want and try and try again.

It's a good idea to grab armor early by making the jump across the gap in the first room. One thing to keep in mind is that while your health maxes out at 50 you can get a health boost in the cave if you follow the water below the bridge, but more importantly that this health boost will respawn so you can grab it whenever you want/need it.

The first area is simple, charge the soldier on the right as you leave the corridor, then jump across the gap on the left side of the room to get to the higher part of the room and charge the soldier there. Grabbing the armor before going back to the gap and through the nearby doors, charging the soldier at the elevator.

Once down the elevator you can attack the soldiers close to you, strafing and backing away to avoid gun fire when necessary and keeping a few enemies in front of the rear enemy to soften the others up. One may remain across the bridge but you can use corners of the bridge for some cover before running across the bridge to attack.

Once this area is clear you'll want to clear the cave mentioned previously, grabbing a health boost, following the water to another elevator returning you to where you got the armor. Retrace your steps, go across the bridge and hug the wall to the left of the doors before opening them and drawing enemies outside. Keeping a few in the line of fire while axing the ones getting too close. You may want to back up after each strike on a dog if you need to fight them. Going further inside to get any stragglers still on the other side of the doors.

After killing the enemies in this entryway you'll follow the wall opposite the doors until you are faced with a large gap and enemies across it. You need to hit the button to extend a platform to walk across. Here you can try getting them to shoot each other, attempt to draw them to you around the corner, or strafe and dodge to get close enough to axe a few of them.
One thing that worked once was leaving the area, returning to the health boost cave, and after a while returning to the button. They seemed to have moved back down a corridor on their side of the gap. After approaching the corner across the gap they began to fire but with the tight space they ended up killing each other for the most part leaving one to be axed.

Here it may be useful to take advantage of Quad Damage found by striking a reddish stained wall in the corridor before the ramp leads downwards. There are three buttons to hit along the way down the ramps but near the third button a group of enemies reside further down the ramp. It may be possible to alert them and retreat up the ramps a little, causing some friendly fire before you can mop up the rest quickly with Quad Damage.

When everyone on the ramps are dead go to the right of the door at the bottom, where there is a column with a biosuit behind it. Grab the biosuit and dive nearby, finding an underwater path that follows the path behind the door opened by the three buttons. Following this will end in a space above in which to surface where you will find health packs and armor. These should help with the final stretch.

With the armour you just got, and maybe a health top up from the cave, you should be able to clear the corridor after the door, allowing you to run, hop and chop the rest of the way to the exit. You'll need to take some damage as you go but hopefully you'll have enough armor and health to deal with it.

you can use the console commands with PC as this game is play anywhere title and get this one nice and easy

fear not xbox players, here a simple(ish) way of getting this achievement.

hello and welcome today we are going after the achievement slipgate pacifist so a few things before we get into it #1 you can kill enemies you come across you just gotta use your melee weapon #2 monsters even more deadly on nightmare having faster reaction times and attacks #3 health kits do not heal you if you are above 50 hit points so keep this in mind this achievement can be difficult heres a video for guidance


1) start the game normally head through the normal portal into the episode 4 area and into the water make sure to land on the beams that are there as they lead to the secret nightmare difficulty

2) head left towards the elevator kill this enemy head down the elevator

3) head to the right and fall down into the water kill the enemy guarding the megahealth pick up then follow the path to an elevator that takes you back to the start

4) pick up this armour kill the enemy in your way and head back down the elevator again

5) dodge any enemy not in your direct path head across the bridge and through the doors on the other side

6)take a left here dodging everything in your way you will come across a switch on your right hit it cross the bridge that comes up and continue on

7) head down the path hitting every switch along the way there are 3 total to open the door at the end

8) just keep following the path dodging enemies

9) once you get around the corner there are 4 grunts guarding the top of the ramp just hack your through them and as soon as theres a clear path to the exit run for it