Mission 8: Advanced Research Complex

Your goal is to meet up with Samuel Hayden. Exit the hall and go upstairs. A Mancubus will be slaughtering some Possessed in the far distance. Wait for it to move around the corner and take it out with rockets from a long distance.

Continue down the hall and check out the second (female) restroom. There's a ventilation shaft in the ceiling, so hop onto the sink and double jump towards it. This may take a few attempts, but you'll get the hang of this particular double jump forward soon enough. Go through the tunnel and drop down at the other side to find an Elite Guard and an AutoMap. Unlock the door with the panel and defeat the Possessed on the other side. You're now picking up the main storyline again.

Mission 8 - Elite Guard #1 and AutoMap

Go inside the security room and collect the Argent Cell, then hit the panel to unlock the door up ahead. Defeat the Possessed, go upstairs and kill the Possessed Soldiers (including a Security - use the Rocket Launcher), plus a Hell Knight. When the coast is clear, grab the Data Log and hit the panel on the receptionist desk to enter the next room.

This is a Gore Nest area - unfortunately for you! Take note of the many pickups in the area, including a two fuel (so you can saw a Mancubus in pieces next up). There's also a Berserk powerup to the right. Kill the Possessed around the Gore Nest and destroy it. Grab out the Super Shotgun for the first portion of the fight and start wasting Imps with it. When two Mancubi show up, destroy one with the Chainsaw and the other with the Rocket Launcher (use the lock-on if you have it). After this, kill a few more Imps with the Super Shotgun. When the Possessed Securities show up, quickly move to the Berserk powerup and start defeating them, along with Hell Knights, Revenants and even a Summoner (definitely get it ASAP). If it runs out too soon, finish the rest off with rockets (securities) or the Super Shotgun (Revenants).

Collect all pickups on the various levels of the room, then continue through the upper door. Continue and you'll meet Samuel Hayden. Follow him to his office, grab the loot and continue to the elevator.

In the hall down below, collect the Data Log right in front of you. At the intersection up ahead, check out the room to the left to find an Elite Guard. Continue through the halls and defeat the Possessed here, then go through the door.

Mission 8 - Elite Guard #2

You've reached a Gore Nest area. Approach the main square and several explosive Possessed show up. Back away from them and kill each one, then make your way to the nest and destroy it. A lot of demons show up, including a new type of Mancubus called the Cyber-Mancubus. Use rockets on it to quickly defeat it. Use the Super Shotgun for crowd control and Revenants. After defeating the horde, use the panel in the control room to clear the force field.

Before going through the new opening, check out the nearby airlock door. Behind it you'll find a Rune Trial. In this trial you'll need to defeat 15 demons (among which Imps) before the times expires, and you can only move 3 seconds per kill. In the ('real life') area with the trial you can also play a minigame on the arcade machine.

Back outside, jump to the rocks from the new opening where the forcefield was previously. There are a LOT of secrets in this area, so tread slowly. There are also various Lost Souls that spawn as you progress, so keep your assault rifle ready. Jump to the rocks, then to the left and check out the green light on the rocks to the right, then climb up to reach an armor. From here you can jump to the central rock pillar. Look down to the left and you'll spot a walkway and a pipe. Look down to the right and you'll see various pipes down below as well as a hatch that opens and closes. On the same level as you, up ahead, you can spot a green walkway with a Megahealth behind it, and to the far right side you can spot a lever for a Classic Map.

Whatever you do, don't drop down to the hatch, because that triggers a checkpoint and closes off all possibilities of getting the secrets in this area.

First of all, from the central rock platform, head down to the left side with a (double) jump and follow the pipe to the end to reach an Argent Cell. After collecting it, jump back to the rock formations and climb back up to the central rock platform.

Mission 8 - Argent Cell #2

From the central rock platform, jump to the green walkway with a well-timed double jump. Before collecting the Megahealth, quickly turn around and waste the Cacodemon that spawns. Grab the Megahealth afterwards. From here, looking over the ravine, turn left. Now here comes the tricky part: The rocks to the left aren't exactly steady ground, so once you move onto them, you'll pretty much start sliding down. You need to jump to them anyway, then perform a double jump to the next rocks and then double jump one last time to make it over the pillars to the far end, allowing you to reach the Classic Map lever. It's not an easy jump trajectory so try it several times. Once you've pulled the lever, head back to the area with the Gore Nest to find the Classic Map.

Mission 8 - Classic Map Lever

The last secret is easier to get to. From the central rock formation, simply (double) jump down to the pipes and head right. You'll spot a cave to the left. Enter it to find the Phobosguy collectible.

Mission 8 - Phobosguy Collectible

Now that you've found these secrets, head through the hatch and drop down. Here, look for the green lights to jump onto the small metal beam above and from here climb up to a hatch. Move through the hall, defeat a few Imps and reach the second ventilation shaft area (marked, conveniently, by the number 2). Look for a switch and hit it to stop the ventilation system. Go inside and make your way to the end of an adjacent small ventilation shaft to reach a Field Drone.

Mission 8 - Field Drone

Go back up and head to the switch again and fly up in the large ventilation shaft. Up ahead you'll reach an intersection in the small vent shaft. To the left is some armor, straight ahead is simply the first ventilation and right, through the destroyed fence is the next area.

Turn right. When out of the vent shaft, look left and search this room for an Elite Guard. Head inside the BFG labs afterwards.

Mission 8 - Elite Guard #3

Destroy the Possessed in the main hallway, along with another Cyber-Mancubus. Enter the Prototype Lab 01 and defeat the Possessed inside. Jump onto the equipment in the middle of the room and spot a ventilation shaft to the side; jump to it and go to the end to find a dead body and the Pinkguy collectible.

Mission 8 - Pinkguy Collectible

Go back to the main hall. Enter the Server Room to find a Data Log. Back in the main hall, go to the Prototype Lab 02 and collect the Data Log. Head inside the Security Room (from the main hall) to collect the Corpse Upper Torso. You can use this on the retinal scanner in the main hall, in the middle, to reach the BFG chamber.

Quickly jump on top of the BFG platform in the middle and then quickly to one of the platforms on the side. Lasers will demolish you should they touch your body, so avoid them. Shoot the fuses to destroy the system. Hop to the middle to collect the ultimate weapon, the BFG-9000 (Big Friggin' Gun). It is a special weapon, similar to the Chainsaw, and equipped by Triangle. A full hit will destroy any target immediately and also damages nearby other targets. Ammo for it is rare, so you should rarely use it.

Go through the next door. Clearly the game wants you to use the BFG on the demon horde, although you can also save ammo and simply destroy them by shooting the explosive barrels. Use the console in the middle, then first head right to Testing Chamber 1 where you can find a Rune Trial. Defeat 8 Imps with Glory Kills within the time.

To finish the mission, continue to the Lazarus Labs. Defeat some demons, then approach a Gore Nest area. This room contains two BFG rounds, so you can use it twice whenever you deem it handy (always on very powerful creatures, obviously). After the first demon horde has been destroyed, the forcefields activate and you're left with two Barons of Hell. Two BFG shots will do them in, but you can also try taking one of them out with rockets after defeating the first with a BFG shot or chainsaw.