Sparky Auto-crit Eviscerator
 Zealot Build - Warhammer 40k: Darktide 

This build uses Opportunist in combination with Bloodthirsty  to shred through armored enemies. A single critical special heavy attack will kill every non-boss enemy in the game in one attack with a slight delay (about 1 second for maulers and 1.5 seconds for crushers) while you grind them to finish them off. Then using the special again afterwards grants a guaranteed critical and you can chain this as many times as your attack results in a kill, which should be 100% of the time barring teammate interference. Opportunist triggers from our special attack staggering them in place while we are grinding them.

Special move trick:

When you are latched onto an enemy with the special dodging will end the animation, but you can also sprint forward and slide without ending the animation, this is particularly effective against packs of gunners/shotgunners or ranged enemies in general since you can latch onto them without getting blasted. Note that your view is kind of locked onto the enemy you are targeting so you won't be able to change your slide direction.

Important Nodes:

Enduring Faith : because we can crit on command we'll keep this up all of the time without needing to invest into critical chance

Invocation of Death :another crit payoff/obvious choice

Thy Wrath be Swift :having a special get interrupted by stun can be devastating

Holy Tools :faster kills on armored enemies

Retributor's Stance / Enemies Within, Enemies Without : these provide us with toughness regeneration, even the slight delay of killing in this build will still result in us getting clipped by chaff and together these provide up to 17.5% toughness regen per second (likely closer to 10 on average) 

The rest of the nodes are basically just good zealot stuff and not required for the build but these in particular are mostly personal preference choices and the first ones I would swap around if you were trying to fit something in

Out of Pocket : if you want to reload manually that's fine too

Purge the Unclean : we already do a ton of boss damage this isn't that impactful, you could also swap it to Time to Kill for bigger boss damage single hits or Unseen Blade for a kind of middle ground that's useful against armored enemies when you can get behind them and still provides the same damage to monstrosities from behind.

 Fury of the Faithful also guarantees a critical which is a great way to start the chain if it is interrupted. the 100% rending will kill a crusher basically instantly and it also does a ton of damage to bosses. rev the chainsaw, start charging your heavy attack and then activate Fury of the Faithful aiming for the head or back. Another benefit of fury is the increased attack speed which helps with spamming lights against chaff and clearing them quickly. You could run Chorus of Spiritual Fortitude, but you would have to prime your crit chain on regular enemies ahead of time and I feel like it interrupts the flow. Shroudfield does guarantee a crit but it won't be available as often, and doesn't help with large hordes of chaff.

actually max speed:

replacing Opportunist  with Rev it Up is really fun for going stupid fast, but....... when armor shows up your ttk's are significantly worse. so if you are playing in heresy or damnation I would definitely make this change. Lots of fun