Noospheric Command Tank
 Skitarii Build - Warhammer 40k: Darktide 

This is by far my favourite build for the skitarii. I regularly reach over 800k damage in aurics while also being the tankiest and most mobile skitarii in the team. I've also completed multiple Havoc 40s with it. Forget about using your ability, just keep marking targets for your servo-skull to kill. All of Skitarii's abilities are less impactful than just spamming Noospheric Command on every elite, special and boss you see.

It works best if you have an auto mark mod. Your servo-skull becomes a turret with nearly 100% uptime and you can just focus on staying alive and killing enemies in melee.

The Most Survivable Skitarii Build

While this build is not as tanky as a Fatmangus stealth zealot, it makes up for that in a lot of ways.

• Ablative Wards massively reduces the damage from poxbursters, blight and corruption damage from melee enemies in havoc, pox hounds, getting eaten by beasts of nurgle and chaos spawns, and daemonhosts' corruption aura.
• 3 max health curios helps protect against attacks that bypass toughness/deal extra damage to toughness including poxbursters, snipers and mauler overheads (you still get oneshot by crusher overheads though).
• With Resurgence, Auto-Repair Doctrines, Binary Ballistics Protocol, and Superior Defence Engrams, you replenish around 20% toughness per second. Additionally, Power Redistribution Uplink, Servo-Core Recharge Engine, and Flensing Protocols generate toughness on crit hits (which you do a lot of with the combat blade), weakspot kills, and elite and special kills. A single crit weakpot kill on an elite/special instantly generates 32.5% toughness. All of this combines to make you a powerhouse in toughness generation. It doesn't matter if you have 140 max toughness or 200, you replenish toughness so fast that it doesn't make a noticeable difference.
• You have a ton of toughness damage reduction from Residual Current Buffer, Progressive Plating Matrix,  Threat Detection Imperative, Power Redistribution Uplink, and Flensing Protocols. As well as a respectable amount of damage reduction from Adaptive Combat Engram, Galvanized Coating, and Ablative Motion Routines.
• Galvanized Coating not only provides 15% flat damage reduction but it also makes you stun immune. I consider this mandatory in any build.
• The combat blade provides unparalleled mobility and its high crit rate and attack speed mean you trigger Power Redistribution Uplink, Electro-Strike Conduit and subsequently System Shock very frequently. This crit rate and attack speed is further improved by Servo-Sinew Surge, Last Stand Relay and Uncapped Arrestor. This allows you to very quickly replenish your toughness by spamming light attacks into enemies.
• Electro-Strike Conduit makes up for the combat blade's lack of stagger. It's surprisingly easy to stunlock elites, particularly crushers. You can even hit a bulwark's shield and electrocute them, making fighting bulwarks super easy.
• Because a significant portion of your damage comes from Noospheric Command, you can be mowing down enemies with your servo-skull all while sprinting and dodging around with your combat blade. I cannot stress enough how useful this is. Your servo-skull kills also proc ranged kill talents like Superior Defence Engrams, Threat Detection Imperative, and Galvanic Marking Array. This means you don't need to worry about pulling out your ranged weapon every few seconds in order to keep these talents going.
• Ablative Motion Routines pairs well with the combat blade and 25% damage resistance is a substantial amount.
• The Medicae Servo-Skull allows for clutch revives. Rather than going for a revive and getting obliterated in the process, the Medicae Servo-Skull allows you to revive someone while you continue to focus on not getting cornered or put into an unfavourable position. It has saved a lot of H40 runs.

Why No Ability or Capacitance Generation Talents?

Noospheric Command is a very capacitance hungry ability. Even with four capacitance generation talents, you barely breakeven in optimal conditions. But thankfully, Noospheric Command triggers even when you only have 1% capacitance. In order to use an ability, you'd have to devote between 2-6 talent points (including capacitance generation talents) and still you would have to limit your use of Noospheric Command. As an added benefit, because you'll spend most of your time at 0 charges, you'll also get more value out of Last Stand Relay.

• Advanced Combat Doctrines is bugged resulting in it sometimes draining multiple charges in an instant and struggling to hit moving targets. Even without the bugs it doesn't provide enough benefit to warrant its use.
• Chordclaw Strike is good and feels very cool but you'd drain your capacitance way too much to make effective use of both Noospheric Command and Chordclaw Strike. Furthermore, at least in my experience, using the chordclaw makes me play far too aggressively and I end up taking damage that I could have easily avoided.
• With Voltaic Emitter, you'll almost never be at 3 charges or even 2 if you're constantly proccing Noospheric Command so you won't benefit from the 15 seconds of your attacks electrocuting enemies nor the weapon malfunction.
• Voltaic expander (the base ability) at one charge electrocutes enemies within 6m. In the rare circumstance where you're completely surrounded by enemies and can't dodge out of there, you can use this to buy you two seconds. In the 100 or so games I've played with this build, I have probably only had 2 or 3 instances where using the ability has saved my life.

The main takeaway here is really that by not taking an ability or capacitance generation talents, we get pretty much an extra 6 or so talent points to put elsewhere, while at the same time, completely disregarding the downside to Noospheric Command of the 25% capacitance cost.

Tagging Enemies

• Be aware, lights out missions massively reduce the range that your servo-skull can target enemies. Pox gas and vet's Smoke Grenade mess with the servo-skull's targeting. Psyker's Telekine Shield will block the servo-skull's shots and Telekine Dome will completely absorb them.
• Set your companion target tag to 'press once'. You're already going to be spamming the tag button constantly and your teammates will definitely not appreciate it if you're double tapping tag every 2 seconds. Plus, double tapping is less efficient.
• If an enemy doesn't die in the 2 seconds that Noospheric Command is active, remark the target to reactivate Noospheric Command. This is especially important against bosses. If you don't reactivate Noospheric Command every 2 seconds, you are wasting a lot of potential damage.
• I have tag set to my middle mouse button. Instead of using my middle finger for RMB I use it for middle mouse and use my ring finger for RMB. This allows me to tag enemies while still swinging with my knife. If you're not using your side mouse buttons, it may be better to bind tag to one of them. I can reach comparable uptime/damage without an auto mark mod but it definitely is a greater cognitive load and it gets pretty tiring keeping up with constantly marking enemies manually. Thankfully, even if you don't regularly mark targets, this build still outperforms most other builds.

If using an auto mark mod:

• Apart from feeling a lil dirty and cheaty, the only downside to using an auto mark mod is that it pretty much guarantees that you will never have enough capacitance to use your voltaic expander ability.
• The auto mark mod can re-mark targets for you every 2 seconds to upkeep the Noospheric Command buff.
• Set crushers to low priority (due to their high hp and carapace armor), elites and bosses to medium priority, specials to high priority and trappers to highest priority. Your servo-skull can shoot a dog off you but it can't free you from a trapper net, hence why trappers have highest priority.
• Enable priority switch so that your servo-skull always targets the higher priority enemy.
• Poxburster auto marking should be disabled so that your servo-skull doesn't blow them up in your face. You can always manually mark them if you think you've got the time and space to take it out before it gets in range of you or a teammate.

Curios

Don't sleep on health curios. Please give health curios a chance. With this setup you have 144 toughness and 245 health. Your constant toughness replenishment mostly makes up for the reduced max toughness. With Ablative Wards, you become really tanky, especially against poxbursters. Additionally, taking health curios reduces the effect that the corruption ticks from Ablative Wards has on your health (1 corruption every 20s is a lot less noticeable with 245 health compared to 150). While more toughness does provide better protection against chip damage, its rarely the chip damage that kills you. This build focuses on protecting you against damage that can, in a split second, nuke your health.

• Without ablative wards or health curios, it takes 3 poxbursters to kill you. With ablative wards and no health curios, it takes 4 poxbursters. With 3 health curios and no ablative wards, it takes 5 poxbursters. With ablative wards and 3 health curios, it takes 6 poxbursters to kill you.
• Mauler overheads deal 2x toughness damage, so extra health provides considerably more protection than extra toughness. A mauler overhead with 3 toughness curios leaves you at around 50 health, but with 3 health curios you're left with around 97 health.
• Snipers deal 10x toughness damage. So toughness is virtually worthless against them. With 3 toughness curios, a sniper shot leaves you at around 46 health. With 3 health curios, a sniper shot leaves you at around 141 health.
• Flames from flamers and bombers deal 4x toughness damage. So once again, more health is better than more toughness.

Furthermore, each 21% health curio provides an additional 31.5 health, whereas each 17% toughness curio only provides an additional 21.25 toughness. Therefore, while 3 health curios provide 94.5 health, 3 toughness curios only provide 63.75 toughness.

Perks

• I've tried running 3 corruption resistance perks to reduce the corruption damage from Ablative Wards but found that other perks were far more impactful.
• Given your reduced toughness, gunner damage resistance is particularly important. Due to the diminishing returns, I think 2 of these perks is optimal.
• I've only taken one revive speed perk because most of your reviving will be done with the Medicae Servo-Skull.
• With 3 toughness regen perks and Resurgence, you're constantly replenishing up to 7.125% toughness per second from just coherency alone (without these 3 perks its only 3.75% per second). If you don't feel its worth the extra toughness replenishment, you could swap these perks for max health, stamina regen, or revive speed.
• Damage resistance against snipers, flamers, and bombers are not worth it. While I have mentioned these above as things that can nuke your health, they are not worth wasting a perk slot on.

You could swap out a health curio for a stamina curio if you feel like you're struggling with the combat blade's 4 stamina, but I personally don't feel it's necessary or worth sacrificing a little over 30 health for. I'd try running Evasive Servo Recovery first before using a stamina curio.

Combat Blade

The combat blade provides much needed mobility that this class lacks. This makes a massive difference in terms of your survivability. I prefer the mark VI but the mark III is also viable. Breakpoints are not as important with this build as the servo skull can easily finish off enemies that your knife doesn't kill in one shot.

• Electro-Strike Conduit and System Shock make Uncanny Strike somewhat redundant.
• Adaptive Combat Calibration gives it a little more cleave but if you want more you could also take Shockline Breach Protocol, but I've found this to be a little unnecessary. You could also just swap Adaptive Combat Calibration for Shockline Breach Protocol but I would rather permanent 30% extra cleave rather than 50% conditional cleave, plus you wouldn't be able to take Ablative Motion Routines if you did so.
• Riposte is very important for the build. It helps trigger Power Redistribution Uplink and Electro-Strike Conduit, as well as Flesh Tearer.
• Flesh Tearer helps particularly against bosses. You could take Lacerate but given all of the crit chance this build has, I think Flesh Tearer is more optimal.

Alternative Melee Weapons

You really need a weapon with high crit chance. The only alternative melee weapon that works well with this build is the Paired Transonic Blades because it has access to both Shred and Riposte. I've tried with the mechanicus power sword but it just feels so much worse and does not have enough crit chance to trigger the crit related talents frequently enough. The shock maul does alright, but its not really suited to this build. The same goes for the arc maul.

Ranged Weapons

Feel free to use whatever ranged weapon you like. I prefer one-shot one-kill weapons, particularly the phosphor blast pistol or the plasma gun because every second spent shooting is another second where you're not focused on preventing melee enemies from hitting you.

I was initially using the Phosphor blast pistol but I found that I was wasting ammo shooting specials that my servo-skull was already killing. I decided that the plasma gun was more optimal as I'd just save it for big groups of elites and it's a little more ammo efficient. While the plasma gun does require a fraction of a second to charge each shot, being a hipfire weapon its immune to enemy suppression, and it doesn't require constant reloading (a prime opportunity for melee enemies to hit you).

• I haven't bothered checking whether the 25% flak damage perk actually helps hit any breakpoints, I just chose it out of habit. So if you feel something else would be better, feel free to change that perk.

The heavy laspistol isn't too bad but I don't think its better than the plasma gun or phosphor blast pistol. It may be a more appealing choice if you go with a melee weapon with slower mobility.

Alternative Talents

• Overcharge Transfer Lattice - I rarely notice this talent triggering and it has a long cooldown (15s). If I'm playing Havoc, I swap this out for Shockline Breach Protocol or Evasive Servo Recovery.
• Hybrid Combat Covenant - Unlike Sustained Assault Doctrine (which also gives 15% damage), Hybrid Combat Covenant does not affect DoT damage. So if you were going to swap out a damage talent for a defensive one, I would recommend this one.
• Weakness Analysis Doctrine has really good uptime with all the DoT damage that you deal, though, it only provides 10% damage. Personally, I prefer taking a defensive talent over this. This would also be a decent alternative to Hybrid Combat Covenant, particularly if you are using a ranged weapon that applies burn. Furthermore, this talent also gives you access to Kinetic Energy Distributors 
• If you want more toughness replenishment take Entropic Transfer or Kinetic Energy Distributors.
• If you want better stamina management, try taking Evasive Servo Recovery. Regularly having stamina to perform a push and/or push attack can be very handy. I often run this build with this talent over Overcharge Transfer Lattice.
• If you want to provide more team support take Power Overflow.
• Hydraulic Impact would be beneficial given all the heavy attacking you do with the combat blade, but since you're already stun immune with Galvanized Coating, you're only benefiting from the 15% extra damage.
• If you decide to swap out the combat blade for a different melee weapon, I would consider swapping out Ablative Motion Routines for something else.