Overlord is a mission available as. This walkthrough was written with Shepard as an Infiltrator, on Veteran difficulty. As you may be aware, Cerberus has policies in place that if one of their distant outposts isn't being wiped out to the last man by some kind of foolhardy and dangerous experiment, something is clearly wrong. When you install Overlord, you will be informed via a message at your terminal that, get this, a Cerberus outpost has gone dark and they'd like you to investigate.
Imagine that. You can go on this mission the moment you gain control of the Normandy, if you want, but it's a good idea to leave it off. Every enemy in Overlord is a droid or a geth, which makes anti-shield/synthetic powers and abilities extremely valuable; Area/Heavy Overload and Disruptor Ammo are both amazingly powerful, and AI Hacking comes in handy as well. Garrus, Miranda, Tali, and Legion all make good squadmates here. To begin the mission, head to the planet Aite in the Typhon system. When you land, go through the door directly in front of you and watch Archer's message on the desktop terminal.
Please Enter Your Date of Birth.
Shoot out the nearby window and climb through the frame into the lounge, then listen to the log on the nearby table. Loot the room for 1,125 credits and some medigel. Go through the door, turn right, and use the console to retract the communication dish. You'll immediately meet the rogue VI you're here to deal with, and if you find that inarticulate fuzzbuster of a scream he does obnoxious, turn off your sound now, because there's a lot of it. After you've heard another radio broadcast from Archer, the door on the far side of the room unlocks. Go through it and head downstairs, grabbing 525 credits from a PDA on the floor, and be ready to deal with three waves of increasingly well-armed geth.
This includes a couple of heavies and a few destroyers, but again, if you're well-prepared, this shouldn't be an issue; upgraded weapons with Disruptor Ammo will just shred through anything you run into on Aite. Search the area for a total of 1,700 credits' worth of salvage, then take the tram to go back outside.
As you're making your way along the transmission dish's exterior walkway, feel free to use your heavy weapons if it'll make life easier; there are two separate storage areas here, containing power cells, 1,000 palladium, and a medical station. Once you're inside the dish's maintenance area, you'll need to fight through a particularly difficult ambush. The geth Hunters make a reappearance here, engaging stealth fields and running in to flank you, and the entire center of the room is this huge warren of pipes and stairwells that doesn't lend itself to effective cover. This can be a frustrating fight. When it's over with, climb upstairs to go out onto the dish's surface. Expose and destroy each capacitor's fuel tank, and watch for geth attackers each time you do. As you blow up the second capacitor, a geth prime shows up, which is a good excuse to use up a couple of missiles or your particle beam.
Once you've destroyed the project's satellite dish, Cerberus rewards you with an additional 3,750 credits in mission funding. You'll move on to interrogate Archer. When you're done talking with him, leave the base and get into the Hammerhead. Fortunately, this is not the second coming of the Mako, as the Hammerhead is a hovercraft. It has a frankly ridiculous amount of horizontal air time, which comes in very handy. On the other hand, it also can't take a lot of damage before exploding.
Your goal is to infiltrate two distant stations, which are marked by your in-game radar, and activate two overrides. Prometheus is slightly closer, so go there first. To enter Prometheus Station itself, you have to trick the geth cannon into destroying the four shield generators, which requires you to get it to fire at you while you're sitting behind them. Accelerate to safety the moment the cannon starts powering up, as on any difficulty, one hit from the cannon will vaporize the Hammerhead. Destroy the cannon with your main gun, then go into the station on foot.
Take 800 platinum off a crate nearby as your reward. Go up the ramp to the top level and salvage some lab equipment for 375 credits. Go through the hall and open the left door; at the base of the stairs, turn left for 575 credits' worth of salvage, then right to continue onward. At the base of the next ramp, turn right for another 375 credits' worth of salvage, then left for another research log. In the large room at the bottom of the ship, climb the ramp to find a panel from which you can manipulate the floor panels.
The lower-left button cycles between the controllable platforms. You can move all three to reach a platform with a medical kit, some power cells, and 600 credits, then rearrange them again to allow you to cross the impasse.
Hit the override switch and hack a nearby console for 1,875 credits, then fight your way back out of Prometheus Station. Once you reach the Hammerhead, this stage of Overlord is clear.
Go back the other way and head towards Vulcan Station. Once you transition towards that approach, it's time to start playing with lava. Jump the river, then use the steam vents to give yourself enough lift to reach the ledge behind the station. Destroy the guard turret in the tunnel beyond, then turn left at the fork for 400 iridium.
Turn right to find a much wider river, which you'll need to hop across using the chunks of rock. Sitting on them makes them sink, though, so quickly hover away again before you take a lava bath. Use the vent to reach the security station, then disembark and shoot your way through it to turn on the vent nearby.
Get back into the Hammerhead, then sit on the vent until you reach maximum altitude. Then hover over onto the ledge. Destroy another turret and scoop up 400 iridium from nearby. Ride rocks down the lava stream to reach the next canyon, then use the vent if needed for a well-hidden cache of 400 iridium. There's another cache of 800 iridium guarded by two turrets on a ledge across the canyon, but it is in no way worth the trouble to get. Once you've done all the looting required, hop from rock to rock upstream in the next river to reach the next installation.
Inside, use a bypass on the valve control to reach a datapad with 1,125 credits, then shoot the explosive container to clear the path ahead of you. Keep an eye out ahead, and you can avoid a fight by shooting an explosive container the moment the LOKI mechs ahead of you activate. Fight your way up to the top level.
Open the door for 1,500 credits and a research log. There's a tough ambush from a number of LOKIs, a YMIR, and a bunch of flying assault drones between you and the override. Now you can enter Atlas Station, which you probably found before now, behind the waterfall near your starting point. It's more or less a straight line to start with, although there's a medkit and 1,500 credits' worth of salvage along the way.
The laboratory has an unlabeled puzzle for you. You're on the seventh floor and you want to call the elevator, but it won't arrive if you simply hit the button. There are three terminals you can interact with throughout the room, though, and each one adds or subtracts a set number of floors to the elevator.
To get it to arrive, hit the elevator button twice, then use the security console. This brings up the elevator, which is currently occupied by a couple of shielded geth troopers and a geth prime.
Take them out, then ride the elevator down to find 1,000 palladium, 2,250 credits in a hackable terminal, and a deactivated geth. You can scan the latter to discover a Heavy Skin Weave upgrade. When you try to leave this area, weirdness ensues.
Open the new door and use the console inside to enter a new virtual environment, while leaving your squad members behind. Alone, dispose of a few more geth, then loot the lab for power cells and 500 palladium.
After the flashback with the Archers, shoot the geth's halo to damage all three of the troopers in the next room, then finish them off. Grab 2,250 credits from the wall safe before you leave. The next door is locked, but you can destroy its shielding with weapons fire, then override it. Use the elevator control in the lab to call up the lift, and greet the geth aboard it with a couple of grenades or missiles.
You can then reload using the power cells in the lab, and grab 1,500 credits and 500 palladium while you're at it. Ride the elevator down to finally confront the rogue VI. This isn't an immediately obvious fight. You need to counter the VI's attempts to upload itself to the Normandy by shooting the VR connection globes before they can reach the end of the conduits they're in. This is made a great deal easier if you have Disruptor Ammo and a rapid-fire weapon, as it'll destroy the globes in the seconds. The upload is also very fast, and if you leave a connector alone for too long, it transmits the VI to the Normandy and the game ends.
When you destroy all of the connections in a wave, which is occasionally complicated by the arrival of some geth troopers, the VI core is temporarily exposed. It's armored, so use whatever you've got to most efficiently dismantle it.
Once you destroy the VI's core, a final conversation with Archer ends Overlord. Be sure to try the Paragon interrupt on him at least once.