Mission 4: Argent Facility

Go upstairs and then head outside. Jump towards the lower level of the tower and climb up by going to the ledge to the side first. Climb up to reach the higher rocky walkway. You'll find the first Rune Trial (Vacuum) here, in the form of a green symbol in some glowing, floating rocks. In these trials, the idea is to defeat or destroy a certain amount of enemies/objects to complete the challenge. This one grants Vacuum (a powerup of some sorts, which lets you collect items faster as they are sucked towards you more easily. You must defeat 15 Imps before the timer expires. You get 10 seconds, but each kill grants more seconds, plus 2 extra seconds for Glory Kills, so perform a lot of those.

Head up the steps, go left, go up some more steps on the left and grab the Data Log. Also check out the classic map lever behind some barrels very close by in the left corner and push it. Go through the nearby door and continue to find the Classic Map (Toxic Refinery) to the right, with a lot of health and armor pickups inside. Nice.

Mission 4 - Classic Map

Equip your rocket launcher and open the next door (in the real, non-classic DOOM). There are several demons up ahead, including two Possessed Security. A few rockets should do these in. Switch to your shotgun and finish the remaining enemies regularly, but be warned, there's also a Hell Knight among them.

Continue over the metal debris on the far left side and as you continue you'll spot a Field Drone moving away - we'll get to it in a bit. There's a Gore Nest up ahead, so clear the area of demons first, destroy the nest and finish the rest of the demons that spawn. Of course there's another Hell Knight among them. Of course.

After finishing the demons you can essentially choose from multiple areas. Behind you is the Hangar, the first option. The second area can be reached by climbing the crates not too far away from the blue forcefield (if you face it, they're on the left). And the last area is located on the far right.

We'll begin with some optional exploration. Facing the blue forcefield, go down the path to the left a little bit, then look to the right, down the ravine. There's a ledge here where you can drop down. Follow it down, to the right side and you'll reach the Field Drone we saw earlier. Head back up the platforms, but don't go up all the way. Continue to the right, on a path roughly on the same level, and follow it to the very end to find an Elite Guard. Now head back to the main area where you destroyed the Gore Nest at the blue force field.

Mission 4 - Elite Guard 1 and Field Drone

Head inside the Cargo Station (facing the blue forcefield, turn 180 degrees and go through the door slightly to the far left). Here, defeat the Possessed and grab the Data Log from the corner. There's also a chainsaw here. Go through the other door and destroy the first Argent Filter.

Back in the main area, facing the blue forcefield, go left and head through the door here. Beat a couple of Imps, then move around the yellow machinery to find a very handy Argent Cell. It's recommended to go for Health, but if you haven't upgraded your Max Ammo, that would also be an excellent choice.

Mission 4 - Argent Cell

Head back to the main area. There are a few stacked crates near the blue forcefield. Climb them to reach another Gore Nest. Eliminate the demons (obviously there's a Hell Knight; obviously) and face the Union Aerospace (round shaped) building. The catwalk on the right side of it leads to an Elite Guard. Ignore going further and head back to the Gore Nest that you just destroyed.

Mission 4 - Elite Guard #2

Facing the round building, turn left and go through the door. You're now in the 'Garage' area, upper level. The door at the back of this short hall is where the second Argent Filter is located. Destroy it, then go in the big adjacent room. You can find a Rune Trial (Dazed and Confused) on one of the machines to the right here. You have to destroy 30 barrels in 6 seconds time, with +2 seconds each time a barrel is destroyed. The last three barrels are marked with a red glow.

Back in the regular world, pull open the door in the back of the 'garage' area (same area as where the Rune Trial was) and look for an ammo crate. Later on we'll come back here, but for now the next door is locked. Head down the lift to reach the Cargo Room again. Hop up the stack of crates (these are newly placed here after you destroyed the second Argent Filter) to reach a ventilation shaft. On top of it, walk to the left to find the UACguy collectible.

Head back to the main area and go up the crates and to the left, where the second Gore Nest was. Climb the crates and go through the door on the upper walkway. First shoot a few regular Possessed out of the way, then step back a little and pull out your rocket launcher. It's an excellent way to use this against the Possessed Security and Hell Razors that spawn inside the area, while standing in the doorway or just outside. Head upstairs when all demons have been wasted and turn right to find a Field Drone and a Data Log (on the desk).

Go downstairs and walk to the end of the walkway, then climb up the ledges. Jump over to the other side. There's an ammo crate here. More important is that you can walk on the ventilation shaft on the edge (don't fall down). In the room that you can access this way (to the right, near the end of the vent shaft) is the Stealthguy collectible.

Mission 4 - Stealthguy collectible

Drop down and make your way to the end of the path until you reach a door. Before going through, look to your left, to the shadows. There's an optiona path here that leads to the Super Shotgun at the end. Now go through the door and destroy the demons along with the Gore Nest. When you've done so, check out the far (initial) left corridor on the ground level and open up the closed/jammed door here to find an AutoMap Station in the room behind. On the higher level, go through the door to find a Data Log and the last Argent Filter. Destroy it and head outside; you'll be up against a few demons, including a new species, the Summoner. It can summon new demons (hence its name), so take it out ASAP with the assault rifle.

Go back to the garage (where the second Rune Trial was) and go through the door your pulled open previously. The door here is now unlocked. In the area behind you'll find another Gore Nest. Destroy it and defeat the Summoner and various other demons including a Hell Knight. The Berserk powerup can definitely help for wasting the Summoner and Hell Knight.

Mission 4 - Elite Guard #3

Go through the door and loot the Elite Guard laying on the left side (behind some crates) as you continue. At the end of the linear hall, use the Argent Processor to finish this mission.