Penetrating the Kett Defenses
As you explore (broadly) Eos northwest of Prodromos you’ll be contacted by a Kett named Invictor. His taunting doesn’t impress Ryder - nor should it - but it does highlight his presence to you, and mark him for extermination, a task covered by the quest "Defeating the Kett". As this quest delivers the storyline coup’de’grace on the Kett forces on Eos, ideally it’ll be completed after other tasks, but there’s no real reason gameplay or storyline reason why you need to wait.
When you’re finally read to act on the friendly banter between Ryder and the Invictor, travel to the Sheartop Forward Station and from there drive northwest to reach the outskirts of the base. Part of the base is outside of the barrier that surrounds the majority of the stronghold, and this exposed area is crawling with Kett - mostly Chosen, with a scattered of Anointed and two Turrets. The latter are going to make things more complicated, as they can take a bit of damage, as well as deal it. Just take cover behind some Kett crates and pick off foes as the opportunity presents itself, and deal with any Kett foolish enough to approach.
Defeat the Kett and head up a ramp to reach a Locked Console, which you can unlock. Once you do, immediately take cover, as you have to defend this area from numerous Kett waves, courtesy of dropships. The enemies that will assail your position include Chosen and Wraiths, so don’t expect too much pressure - a good shotgun will serve you well.
Sabotaging the Shields
After the timer ends head northwest through a pair of doors to reach the shielded portion of the base. Immediately fight off a group of Kett (Chosen, an Anointed and Wraiths) then continue northwest to find a console. Interface with it, and note that two navpoints appear on opposite ends of the circular walkways leading away from this location. Work your way over to one and the Invictor will predictably call for reinforcements, consisting of a squad of Chosen led by an Anointed delivered via dropship. Kill them, but don’t venture too far to the northwest, as major resistance awaits you deeper in the stronghold. Instead, sabotage a console, then repeat the process with the second console.
Sabotage the consoles at both navpoints, then return back to the central console and jump up to the platform above, where you’ll find two consoles. One disables the alarms for the stronghold (which should be noted for later on) while the other (a console to the northwest) takes down the shield.
Disable the shield around the Kett base, then drop down to the northwest and continue along a walkway in that direction up some ramps and stairs until you reach the heart of the Kett base. Separated from the previous structure by a narrow strip of sand, this multi-level command center is, fittingly, crawling with Kett. As you approach an alarm will start to blare, which can be deactivated by backtracking to the platform to the southeast, or by using numerous consoles up ahead. While the alarm sounds Kett dropships will periodically descend to harass you, and if you linger after deactivating the alarm it’ll start up again.
On top of that, you’re tasked with disabling three security overrides - one in the upper floor of the multi-floor structure up a ramp to the northwest, while the other two can be found along walkways to the west. You’ll have to deal with endless waves of Kett (Chosen, Wraiths and the odd Anointed) while these security overrides remain unmolested, perhaps in addition to the dropships summoned by the alarm.
Fight your way up a ramp to the northwest, then turn south and head up another ramp. Follow a walkway west, then northwest to find the first security override console near the entrance to a structure to the northwest. Disable it, then head into the structure to the northwest (there’s a console in the western corner of this room you can use to turn off the alarm, if necessary) turn northeast and head up a ramp to reach the interior of the multi-level structure that dominates this part of the base. Turn southeast and be wary of Kett rising up from the floor below - your goal is at the southeastern end of this chamber. Disable the second security console and turn northeast to find another alarm-disabling console, if required.
Slaughter your way northwest down the northeastern end of the room until you find an opening to the northeast, at which head back outside and continue down a ramp. Turn northwest at the end of the ramp and follow a curving walkway until it ends at a circular platform. Look out to the southwest to spot a circular structure below you, beyond another walkway. At the southwestern end of this structure is the third and final security override console. Disable it, then jump up onto the roof that partially covers this structure and turn northwest and enter a chamber with a final console you need to interface with. Do so and a hole will open in the floor, the enemies will become finite, and the next time you disable the alarm will be your last. Now is a good time to sweep the Kett crawling around the base, loot containers, resupply, etc.
Boss Battle - Invictor
When you’re ready to move on, return to the hole you opened up and drop on down to the command center, where naturally you’ll encounter more Kett. Head down some ramps to the south, southeast to reach a large chamber with two floors - Kett resistance will be relatively light in this room, but the Invictor and his goons await in a larger room to the south, southeast. The lesser Kett include a handful of Chosen an the odd Anointed, while the Invictor himself is an Ascendant By now you know how to fight all these foes, and you have plenty of room to maneuver, making this fight even easier than the battle with the Cardinal… especially if you lure him into the northern of the two chambers.
After he’s dead, continue into the more cramped chamber to the south, southeast and activate a console, then continue through a door to the south, southeast. Turn east, northeast and go through a second door and interact with some Elevator Controls, then head north, northwest to reach the command center. Loot two containers, head down a ramp and scan a Kett Core Encryption Tech device, nab two more containers to the north, northwest, interact with a Terminal to read up on some Kett correspondence, then finally use a console to disable the Remnant base. You’ll earn 1,330 XP for defeating the Invictor and later you’ll get a further 300 AVP and +10% Eos viability for disabling the Remnant base. The prospects of successful long-term colonization just increased tremendously.