Gladiator
 Hive Scum Build - Warhammer 40k: Darktide 

You must wear the gladiator style helmet!

Playstyle: 

This is for those who can play hyper aggressive when required. It's the only way to take advantage of majority of this build as a whole. This build is literally meant to front line, but not tank! What I mean by this, is it's amazing to support another front liner and can even front line for the other 3 players with you, but it can not tank at all due to the restrictions of Hive Scum disadvantages. You have low health, low toughness but what you excel at is speed, mobility, and aggression. Hive Scum is really good paired up with an Arbites and Ogryns. They tank, you deal the agro and damage for them. Stagger is great for this playstyle which is another reason why these two pair so well with this build.

An example of this is when a lot of gunners are shooting at you, you can't sit back. You need to dodge, dive and go all in to force them into melee and go crazy on them. Take the aggro for the team but don't get shot, you will die almost instantly compared to the rest of the classes. The reason for this is you stack toughness up with the amount of hits you deal and if they die, even better. To keep it up, you need to throw yourself at them. This is why I am making so much detail on hyper aggression.

Weapons: 

Enginseer's Mk VI Crowbar to me is the best fitting for this build and style. The damage output is not the best, but it's blugeon, stagger, damage and even can debuff enemies with the blessing where required (great for bosses or more single targets for everyone to focus on). With the brittleness, you can turn 50 damage to 100 damage per hit. You can try other weapons but in my experience, nothing gives the same experience for this build as the Crowbar. If you pick a weapon with too much attack speed, the DPS isn't enough to keep you going. Remember, you will be targeting more than one target, so you need to find a balance between the group. I have tried weapons like Atrox Mk IV Tactical Axe with various marks and it's just waaay too fast with too little damage. I end up being stuck in a corner of a room trying to kill multiple elites too slowly and take unnecessary damage. Thus, the balance between speed and damage is required.
Reasons why crowbar is my favourite to use:
1.) The sound it makes when you hit them. Bong!
2.) The attack speed is fairly decent and not too fast when used with your Stimm or your ability. 
3.) Damage is fair across the board against all enemy types.

Branx MkVI Needle Pistol is great to help with shooting a special once, and then carrying on. The damage over time it does is decent enough for you to multi-task and not have to worry about focusing on specials between fights. Melee, swap to needle, shoot once, then back to melee. This is the reason why I go with the 60% on Damage because everything else benefits me in general, but the damage over time doesn't really feel worth the loss of another stat. The blessings are the best combination I have found so far as you want the accuracy to be as good as possible so you can hipfire mid-slide or for quick shots, and then continue fighting. Being immune to ranged also allows for better accuracy when it is required for a single shot too. 

You can technically use other options like the Agripinaa Mk XIV Quickdraw Stub Revolver but I feel like the needle has better advantages over it without having to sacrifice range of either short or long distances and I don't have to really do more than one shot unless I want it dead fastly. Two more benefits to the Needle is actually the ammo efficient use of it and also how effective it is against bosses. Stack up the chem stacks on bosses and you can DoT it to death whilst you focus on the hordes/elites.
 

Curios: 

You require +3 stamina with 2x toughness. Stamina is required to keep up your attack speed as you slice through hordes. When using the Enginseer's Mk VI Crowbar , you can attack block for a really nice cleave. Spending stamina, then also boosts attack speed per missing stamina in the talents. Hyper aggression activated! 
With the lacking total of toughness, it becomes so much more important to stack it in my opinion. We have the worst toughness regeneration of all classes, so why not stack it as much as possible? Every single hit and kill you do, gives you the most toughness. So stacking this allows each aggression moment even more important, especially when it comes to moments of stacks of armour, hordes and elites. You can stack toughness with the horde whilst cleaving or single targeting the elites.
So with my toughness curios, I use the perks to add more toughness for the same reasons as above. 
I then stack Revive Speed on all 3 curios since it is amazing when it comes to reviving in all cases. From death, to downed, all of it. The quicker you can do this, the easier you can stagger/control a zone and quickly pick up and go. Once again, back to being hyper aggressive.
Lastly, I then have damage resistance to gunners for obvious reasons. You are such a target for such things to murder you instantly. This is to massively reduce this. Since I feel like 2 stacks are enough (remember, it's multiplicative, not additional so it doesn't fully stack ontop of each other!) I then take Stamina Regeneration as the last perk on my 3x Stamina. This is to help keep my stamina up at almost all times and situations. This allows for sooo much movement with a little more of that in Talents for why it is important to keep movement up.

Talents: 

So I wont bore with all of it as you can read the specifics but there is reasons for why I picked what I did.

• Boom Bringer seems to be the best blitz for this build. The chem grenades are used way too much but doesn't feel right for a gladiator melee fighter. The stun grenades are nice, but don't really give you much in this build to take advantage of as you want to hit them weak spots. If you want an alternative, use the Blackout. So just incase, do NOT spam the blitz at all. Be precise when you want to use them. I use them in two ways. Firstly, when it is just getting way too surrounded for the team and you just need to instantly clear. Pull it out, aim down (or where you can in the centre of the group) and shoot. Get your footing back in and have a short breather. Secondly, when you truly need specific groups dead asap. This is objective, but you truly need to pick it and not spam out. The only time you can ever spam, is if your 3 teammates do not need grenades. Do not be selfish and work with your team on this. It's kinda OP right now, do not make people hate you for it too. We're here for some fun too, right?
• Rampage! is a must have. You're melee..of course! So attack speed, rending (required) and going nuts. That's all required to know. Turn on, smack heads. Go forward, and repeat. Thing is, the more you smack, the more the ability stays on for maximum output. Stack this with the stimms down below with the keystone as well, you will always have the ability with as short as 20 seconds cooldown between uses.
• Nimble is sooo good for Hive Scum. To keep up, you must keep moving. Mobility comes in so well with further dodges and even longer dodge time so you can keep moving and smacking things. This also massively helps with ranged units. Surrounded? You're not in there with them, they're in there with you. Dodge, smack, smack, smack, dodge, smack, smack, smack and repeat. Do not overdo it with the mobility otherwise you'll dodge into overheads from the elites. That's the only downside, player brain going overtime with not dodging enough.
• Swift Endurance and Hive City Brawler and the reasons why I have the +3 stamina. Take as much advantage of using stamina spent or have left, by increasing attack speed, damage reduction and even additional damage as you keep moving. Win-win in my book and adds to the hyper aggression. 
• Chemical Dependency is great for this. What more could you want from a keystone than to keep stacking cooldown and to make sure your ability is up as much as possible? Well this is it but you need to understand it. The more aggressive you are, the more you pop your stimms, ability and keep fighting. This is what you want, to keep gaining stacks of everything to keep going. Front line them enemies and smack them about. So, after 3 stimms in succession, you get the maximum amount of abilities up.

Stimm Labs:

Biggest reason for this, 69% cooldown. No joke, once I found it, I never went back for this build!
In all seriousness, what more do you want our of your stimms? You have attack speed, rending (Important!!!), cooldown for ability and stamina reduction. I don't need to explain why it is important for this except the rending. You need rending to heavily take our elites. You can not one hit anything, but you sure as hell can stagger and bash everything in. If you want to max out your rending use the stimm with your talent at the same time. 35% rending is really good for base. The cooldown on the stimm is a sometimes too high but not high enough to always need it but your ability is practically always available if you stack it correctly.

If you find any issues with this, I am always up for suggestions but please respect opinions of how it is played, and if not agreed upon.