Eradicator/Biogen Reclamation (D4)

In this level you'll need to remotely operate enemy robots in several places, plus it has one of the more interesting layouts in the game. In the first room is an LSD behind a forcefield, and a remote-control console. Past this room you'll come across a set of trip-beams that'll close a security door ahead. You'll need to disable these beams to continue. (The security-door reset switch is next to the LSD cage.)

Remote vehicles
Go to the console and activate it to power up and remotely operate the LSD behind the forcefield. The enemies don't affect trip-beams. Pilot the LSD through the following room to a chamber with dirty fluid and a power conduit. Fire the LSD's weapon at the conduit to destroy it and disable the trip-beams.

Tip: Whenever you're piloting an LSD or HSD like this, you can use its weapon to destroy other enemies in the areas you haven't reached yet. How sly! In the room with the security door, for example, there's a gun turret on the ceiling you can get out of the way before even going there yourself. (Just for yucks--or to be stupid, try shooting yourself with them too ... maybe not.)

(It's possible to get past the security door after tripping it if you use Adrenaline Catalyst to increase your speed. But you might need to run around a lot later on in fluids that cause injury if you do this, because there are no reset-switches on the other side and the LSD you could have used will be trapped unless you moved it beforehand.)

Sewers and forcefields
Park the LSD somewhere out of the way, go to the room with the security door and hit the switch to power the other door. Go through this door to a U-shaped room. To your left are two destroyed floor-to-ceiling recessed light panels. There's a secret area behind the right-hand one. Inside the door to your right is a tall chamber mostly filled with fluid. This area is the sewer. Go instead to the far end of the U-shaped room. In the next room is a passage blocked by a forcefield, and another remote-control console. Hit the switch on the other console in here, and the sewer chamber back around the corner drains (check it out on the PIP), and a passage below opens.

You'll need to get the forcefield down. Use the remote-control to pilot the LSD (you'll get a new one if you killed the first) down the chamber to the opened sewer, to a small room with a grating. Past the grating is where you need to go, but there's a nice side area nearby. Shoot out the brighter-than-average part of the wall to the right of the grating to reveal a secret passage. At the end is a tall chamber with a shootable switch which temporarily fills the chamber. At the top is an air duct back to the first chamber. Back inside the secret passage is another brighter-than-average shootable section of wall, with a teleporter inside that goes to the tall pillar back in the first chamber, another secret area. Of course you'll need to run through here yourself if you want the items, but you can explore everything first with the LSD and not take damage from the dirty fluid.

Back in the room with the grating, take the LSD to the passage past the grating. To the left are two short passages with gratings. The leftmost leads to a deep shaft that's fatal if fallen into. This is a good place to dispose of LSDs you're done with. Note that there's a Deep Radar Tracking right in front of the shaft. The other left-hand passage ends at the bottom of a waterfall (dirty-fluid fall?). Go to the end of the main passage to a tall chamber and shootable switch, like the secret one further back. (Tip: Use the LSD's weapon to take out the HSD in here and others you come across.) Hit the shootable switch to fill the chamber. At the top is a power conduit and a passage blocked by a forcefield. Destroy the conduit to deactivate this and the other forcefield near where you (the player) are. The passage beyond leads back to just beyond the first forcefield. If you run off the bridge, you'll see it's at the top of the "dirty-fluid fall" you saw earlier. You won't need the LSD anymore; you might want to take it to the deep pit to dispose of it.

Past the disabled forcefield, the left-side passage leads to your next objective. But before you continue, go the right-hand way to where you were with the LSD. There are items everywhere throughout the sewer, and with the Invulnerable on the bridge you can avoid injury from the fluid. When you're done here, take the left-hand passage past the forcefield to the upper end of a big fluid channel, with a control area. There's another remote-control station here, this time with an HSD. The Mazrium platform (the switch activates it) goes down the channel, but there's a forcefield in the way; the console by the remote-control shows it. (There's a full-health hidden behind this console.) If you try to take the platform you'll just fall into the muck.

Activate the HSD and pilot it down the channel. Look for a grating to the left, shoot it and destroy the power conduit in the chamber inside to disable the forcefield. If you fly the HSD past where the forcefield was it'll be destroyed, a useful way of disposing of HSDs you're done with. Now, take the Mazrium platform to a similar control area at the far end of the channel, and on to a room with an unpowered door and an air vent up on the wall.

More remote-controlled fun
Your next task is to power this door. The doorway next to the vent leads to a large, very tall and deep, room. (Look on the right-hand side of the doughnut-shaped corridor for a diamond-shaped patch on the wall that's darker than the rest. There's a secret area inside.) This room has suffered some damage. The control room at the far end is well out of reach due to destroyed walkways. Where you'd expect an activation switch for the Mazrium platform near the entrance, there's a smashed spot on the wall instead. Down on the floor you'll find a teleporter inside the door in the column. We'll get to this in a little bit: remember it because there's a trick you can do here that will substantially simplify a later task.

Take the walkway along the inside wall of the tall/deep room to a switch that cycles the platform. Activate the platform, jump to it when it gets close enough, and take it to the out-of-reach control room. In here there's yet another remote-control station; the HSD it operates is just outside. You can probably guess where you need to take this; the console next to the remote-control will clue you in.

Activate the HSD, fly back out to where the unpowered door is, and (you guessed it) go through the air duct on the wall. Hit the shootable switch in the next room to power the door. (Also, take the HSD beyond this room and get rid of all the bad guys and gun turrets you can get to.)

Preemptive measures
Now for that teleporter in the column. Fly the HSD into here first and waste the enemies. In here is a large room, each end closed off by forcefields, with a bunch of LSDs and HSDs behind them: a staging area, it looks like. While you're working on the level's final puzzle, these guys will be teleported into the area a few at a time. You can get rid of them now and make that final task a great deal easier. Here's how: It's possible to get weapons-fire past forcefields to a limited extent. First, take the HSD out to the fluid channel and dispose of it. Then come back here yourself and fire a few shots to get them roaming around. Fire missiles at the forcefield when they come up against it. Try aiming for the holes in the forcefield, at an angle about ten degrees from perpendicular, and a bit below the HSD/LSD. You'll probably waste a bunch of missiles in the process, but there are more in the side room along with additional ammo, and quite a few throughout the level. Alternatively, use the HSD while you have it in here. Get up against the forcefield and aim for the holes and a little to the left. You'll find you can get a few shots through when it's facing just so, but then subsequent shots will impact on the forcefield until you move and and re-aim. This method will take a long time, but you won't use up any ammo.

Beyond and outside
Back to our regularly-scheduled mission. Go through the door you powered up, to a small sunken courtyard. Hit the switch in the sunken area to power the door at the far end. (There's a secret area past the back wall of the compartment on the wall.)

Go inside the door you powered up. Look for a bright patch on the wall to the left of the air vent: there's a secret teleporter inside leading to the control room you're on your way to. Take the air duct instead. Partway through, there's a vent to the right with a Weapon Enhancement Chip inside. The air duct leads out to a big courtyard with three towers and a bunch of gun turrets. Stand inside the vent and use your missiles, which have homing capability because of the Weapon Enhancement Chip, to take out the enemies and turrets (switch the PIP to see what they're shooting at). Now, jump down to the courtyard. In addition to the towers, there's a big closed door, and a steep ramp to an overlooking control room with four teleporters and a switch on the console. That secret teleporter you found a minute ago leads here. The leftmost teleporter goes back to that room with the air duct and secret teleporter.

Solving the puzzle
The final objective is a combination puzzle. The three rightmost teleporters in the control room each lead to one of the towers. Inside each tower is a switch. (When you teleport to a tower, look behind you for ammo and items.) When the correct switch or switches are on, hitting the switch on the control-room console will solve the puzzle and open the big door outside. You'll need to try different combinations until you get the right one. A wrong combination sets off an alarm. Here's the neat thing: normally it'll also teleport enemies in from the staging area, but if you went there earlier and blew them away, there won't be any to teleport and bother you here!

(To simplify things a bit, ignore the "Lock One", "Lock Two" and "Lock Three" labels, and go by which teleporter you took: left, center, right. There aren't many possible combinations, and you can do them in a pattern to speed things up: left, left+center, center, center+right, right, left+right, all three. There's a similar but bigger puzzle with more switches later in the game; this will give you an idea of how to more efficiently solve that one.)

When you get the door open, go inside and up to the overlooking room, where the level exit is. Those three switches on the wall don't do anything: they're just showing the combination to the door. Maybe the idea is the door's combination is programmed from here by the bad guys. Behind the crystal-egg pylon next to the exit elevator is a secret area. Also, before you exit, go back to the staging area. The big forcefields are down now, and there's a load of ammo inside where the enemies were. (You probably saw it while you were here earlier.) Collect this, because you'll need it in the next level. When you're done, exit the level and get ready for the game's first boss fight!