Attention, scum! You are in defiance of the Emperor's law. You cannot hide. You cannot escape. We are judgement. Prepare for sentencing!
Break the line has a 20 second cooldown (12 if you elites). Spam the ult almost on cooldown. This gives you dog almost 100% uptime with "Kill Order", making the dog an incredible killing machine. You get almost every single dog buff ability. We don't have any spare points to get "Serrated Maw" (gives dog brittleness on attack), but you are better off skipping it to instead get "Monstrosity Hunter", for a faster time to kill Monsters. When you use the dog explosion make sure you have your bolter out. It triggers the "Puncture" blessing multipule times, and absolutely melts anything at the cost of a regenerating blitz.
Double barrel mayham. When you hit Castigator's Stance you can often shoot six (or more) bullets without having to reload. Provides good DPS against any type of enemy. The only weakness is distance gunners, but you retain the dog for these threats, and he is specialized to take them down faster.
The shields provide incredible defence against everything. Monstrosities provide some challenge, but you can use your (regenerating) impact grenades to stun lock the monstrosities as you and your team blast them down.
The Shockmaul becomes an incredible weapon with this build. The special/stun attack can kill Crushers as long as you hit them once before to apply the stagger effect on them. This loadout gets Shock Mines every 60 seconds, so don't be afraid to use them.
The key to this build is to fire the special/fire shell out of the shotgun into hoards. A couple of these will get you to max stacks of Terminus, which makes your axe become a blur as it sinks into the heretic skulls.
Both the Voltaic Shock Mine and Arbites Grenade are crazy powerful, and easy/intuitive to use. If you give up the dog, you get to regenerate these every 60 seconds, which provides amazing utility. Remote Detonation can be a bit finicky with getting your dog in position, but provides a great source of stun on monstrosities. It also uses your ranged weapon blessings with each shock, so you can apply multiple instances of puncture for massive bleed if you are using one of the Bolt Guns. It's also a great tool for grouped up gunners if you don't have a great ranged weapon or if they are busy suppressing you.