The Non-Negotiables
Trunk Skills
Calamity Tree:
What Burns Within - fairly self explanatory. Since we're going to spamming 
Dragon's Breath, boosting the damage output of this skill through incendiary damage bonuses is going to pay dividends
Wield the Storm - boost status damage (our DoTs) that we're gonna be spam inflicting onto the enemy
Gut Punch - since we're going to be making good use of the 
Slippy, especially when killing bosses, being able to boost our damage through the extra damage buff from Gut Punch is going to synergise very well with our burst damage capability. We're also going to be spawning a forgedrone from 
Tempered Pyre that will be doing melee damage to enemies on the field too, proccing weakness on them as well which continues the debuff loop.
Bullet Storm - this is an all purpose build, and as such, you can swap out your weapons and enhancements to fuel a DoT style mobbing build as well. Since you'll be applying status effects as a result of this simple gear swap, you can maintain a consistent gun damage bonus from this skill.
The Best Defense - since we're using the Slippy AND Tempered Pyre to be dealing melee damage, we can more or less consistently have a free overshield on us at all times to keep our surivivability up.
Branch 1
Berserk - Source of additional elemental damage
There Is Only Red - further boosts the damage output of Berserk by scaling our cryo damage up exponentially
My Touch Is Death - Once again, the combination of Tempered Pyre AND Slippy means we can maintain our stacks of kills skills i.e. There Is Only Red very consistently, and without much additional effort. Also guarantees a damage bonus during boss fights as well if trash mobs arent spawning as frequently as you would like.
Branch 3
Dragon's Breath - the star of the show and how we apply some big fire DoTs to enemies. This skill adds a huge damage bonus to our first shot following an ordnance activation.
Fists of Stone - helps to cycle AS faster again. Spamming 
Stormcutter and hitting a minimum of 4 enemies with it will immediately give us 
Onslaughter again.
Electrical Fire - Since the base element of the maliwan shotun we're using is shock, this will also help us apply fire to the enemy as well. If you're using 
Linebacker shotgun, we can apply shock dots conversely.
Cybernetics
Gathering Storm - fairly obvious skill to pick up here. Amons damage sauce draws a lot from elemental damage, so we boost this stat where we can.
Tempered Pyre - as mentioned earlier, Tempered Pyre spawns a forgedrone that does melee damage, meaning we can get free procs of Gut Punch and The Best Defense without having to do anything ourselves.
Destruction Engine - more detonation damage means more AoE mob clearing capability (and also to finish off any bosses with max prime stacks using Stormcutter - if they're still alive after bursting them with your choice of ordnance/weapon)
Augment + Capstone:
This spec can give you the option to use whatever augment you have access to in the 
Cybernetics and Calamity tree. However the most optimal configurations would be either:
Optimal option 1
Force of Nature augment to prime enemies in anticipation for their eventual detonation through death or Stormcutter application. These detonations deal massive damage to the enemy and those around them, which furthers the fuel for this mass mobbing build.
Optimal option 2
Axe and Stone + the 
Viking class mod to further fuel an ordnance spamming build through leveraging cryo axe detonations. You also get the added bonus of getting increase movement speed through incendiary axe detonations as well if that's your preferred poison as well. Lots of choice!
Amon
Onslaughter
