Psykitty - Voltaic Vampire
 Psyker Build - Warhammer 40k: Darktide 

Powerful build that will push you, near infinite ceiling.  Empowered Assail + Malefic Momentum = melee beast + toughness recovery.

Horde:
Hit the first wave with back-to-back VoidBlast uncharged secondary attacks to spread SoulBlaze until you start to overheat, then hit your ability and mix alternating between VoidBlast and assail until you start getting up to medium heat, then switch to your sword and start cutting the hoard down, mixing in assail for free toughness regen via Empowered Assail.  You feel invincible until you're not.  Usually at this point you can work in a (90+% heat) Warpshock to finish the hoard off.

When the heat starts coming back down switch back to using you VoidBlast secondaries, primarily for spreading SoulBlaze but also charged longer to knock Ogryns down and then decapitate them with the GreatSword.  It really shines in boss and monstrosity fights.  Try to keep SoulBlaze on them, it might not seem like much but it adds up.

Some notes about the Mk VI GreatSword, it has a complex movements set with undocumented attacks hidden in the paterns.  3x lights, then a heavy will result in a very heavy hitting high cleave L-to-R attack this is how you clear hoards so quickly when overheating.  When you switch weapons to your sword, it will be "unsheathed" from the left before being lift up on your right shoulder, if you attack quickly enough, light or charged, it will start with a faster L-to-R attack, quick-draw Iaijutsu-like.

This build does it all, except overwatch but it can shoot down a sniper if it really needs to with either aimed Assails or VoidBlast rapid-rapid fire primary.