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 Hive Scum Build - Warhammer 40k: Darktide 

This build is a work in progress.

The idea behind the build is simple. Keep as many enemies infected with Chemical Toxin as possible, and reap the benefits. Additionally, drop your Stimm Supply repeatedly to give yourself and your teammates the benefits of your Stimm Lab choices. Whenever that's not available make sure to pop the stimm on yourself so that when it refreshes you get another charge of Stimm Supply.

The playstyle and rotation will be using our melee to apply as much Chem Toxin as possible through melee hits and crits. Our grenade will make short work of the crowd if we start to get overwhelmed. Dropping our Ability and popping our personal Stimm will be detrimental to staying in the game and keeping our ability rolling out as muh as possible for the benefit of the entire team. 

Top to bottom reasoning:

Weapon Choice

Chirurgeon's Mk IV Bone Saw

This weapon provides an additional way of keeping enemies infected. The more enemies we have infected, the more damage we do and the less damage they do. Heavy swings on Chirugeon's will make short work of hordes, and the special ability on the weapon will help to shred Crushers quickly and effectively. 

Critical hit chance was chosen in order to maximize the potential for adding the most Chemical Toxin stacks as possible. Our pip later in Coated Weaponry will apply an additional stack of toxin when our weapon critically strikes, so I wanted to maximize how often we crit. 

Damage to carapace enemies is important for taking down the heavy armor which is just not affected by toxin as much as everything else (not to mention run enders in their own right). This, paired with the special ability, will make short work of crushers.

As for the abilities Refined Lethality helps us to clear Monstrosities and Crushers faster when they are infected, and shred will help us with horde clear.

Branx MkVI Needle Pistol

While I had considered the bolt pistol for removing problematic ranged enemies, I think the NP will work better. Not only will it apply Toxin to our ranged threats, but the weapon abilities will help us close the gap to them. 

Because of this, 1-2 stamina was chosen to pair with our abilities, helping us survive closing the gap, mainly with the Hive City Brawler talent tree perk. After shooting a ranged enemy, we can begin sprinting towards them with hightened damage reduction. 

Increased sprint efficiency with this as well. 

Ghost is here so that when we normally hit a ranged enemy in the head, we can ignore them for a little while. Sometimes we just won't be able to rush them for melee damage.

Stripped Down helps us further close the gap during the initial charge towards the enemy. So long as we have over 50% stam, we don't have to worry about hits. 

Curios

*Requires testing*

Two toughness and one stamina for right now. Two stamina and one toughness might be better depending on how strong the build plays overall. Pips are ability cooldown to drop it as much as possible, toughness in case we get hit, and stamina regeneration so we can benefit more from both hive city brawler and all of our dodges. 

Talents

We'll move down the left hand side to maximize not only our melee damage (and toxic application), but also the ability to close that gap with ranged which seems to be this build's big weakness. 

Chem grenade was chosen as our blitz. An argument can be made for the others, especially if you apply the Pocket Toxin perk. However, Blackout has an incredibly small range of effectiveness and I thik the Pocket Toxin perk would be wasted there. Boom Bringer and Pocket Toxin can be used in tandem if you really want, but I find the Chem Grenade is wonderful on it's own for synergizing with the rest of the build. 

Next we can zigzag here, but depending on what you feel your weakness is as a player, either Nimble or Slippery Customer can be selected. I myself prefer Slippery Customer but when I get more time with the build I may switch it over. Sliding usually puts me out of range of melee swings but if the immunity helps to carry objectives without dropping them when hit, it might be the better choice. Jittery is the best choice here because this build isn't made to stagger. 

Our Aura will be Anarchist. Increasing our crit chance will, again, increase our infection rate. One could make the argument for more melee damage, but I prefer to be more consistant with my toxic applications, and we'd need to lose an extra ability later in the tree.

Our Ability will be Stimm Supply with all three pips. Not only will this apply toxic when it explodes (sooner during engagements maximizing how many it hits), but it will also be up faster when our personal Stimm applies and MOST IMPORTANTLY give our teammates the effects of our personal Stimm, which will allow us to provide overwhelming support to the team not only in damage but also in damage resistance and toughness regeneration (as well as the standard corruption clearing).

We'll then take all of the right hand side so that we can maximize our Chem Toxin benefits, and ove straight down into Dependency to maximize our Stimm Supply regeneration and usage. 

Lastly with the remaining points, we'll move into the center tree to take Punching Above One's Weight, Hive City Brawler, and Hyper-Violence. Depending on how well you are doing and how good the ability ends up being after the nerf, Hyper-Violence can be traded for Tis But A Scratch to help with the ranged enemy weakness of the build. 

Stimm Lab

Our Stimm Lab choices are picked to not only maximize our damage and toxin application chance, but also our damage resistance and toughness regeneration. So the top left and the toughness regeneration over the flat toughness gain, and the top right tree the critical hit chance. 

An argument can be made here for the bottom right cooldown reduction tree instead of the damage, but really in high Havoc and Auric I myself prefer the damage to kill things faster. We can sit and spam protection abilities all day but if enemies aren't going down we won't last long.