Thrusty Tank Zealot (Havoc 40)
 Zealot Build - Warhammer 40k: Darktide 

This Zealot Build covers all areas and is an excellent flex support role.  With the Catachan Mk III Combat Blade you can deal with specials, elites, bosses, and hordes while having the mobility to pivot and position behind enemies to make use of Backstabber.  The bonus damage is noticeable and helps you clear harder enemies for the team.  Beacon of Purity is honestly a must have for high havoc runs as the corruption from enemies can lead to them flat out dying as opposed to going down.  Chorus of Spiritual Fortitude is the main support talent here since you can CC enemies all around letting your team deal with threats while you also make them hard to hurt or kill.  Holy Cause is there since it counters enemies that ignore chorus or the Final Toll modifier which means that your golden toughness is harder to break.  For armor packs or walls of them with hordes, the Artemia Mk III Purgation Flamer has you covered.  It will make all of them take more damage while also clearing out any flak enemies instantly.  This combined with Blaze Away and Penetrating Flame means that nothing will survive your flamer if you let it rip into a horde.  If something does live, it will be a boss or a very weakened armored enemy.

Some modifications to the build could be made, but that is on how you want the knife to perform and what you are building into with a variation to more damage to bleeding enemies or causing enemies to bleed so you can crit faster. 

Give this build a spin and make sure to get back stabs as much as possible, I hope you enjoy it.