This is my own original build, designed around a high level crowd nuking monster

CORE FEATURES:

Shield-gating:
[Harrow] is a frame that has access to high amounts of shields in minimal time due to his condemn ability, this also doubles as his primary source of crowd control... I have abandoned this.
Ensnare has been subsumed over Condemn for mass CC and enemy grouping that is being relied on for our crowd gas nuke.
If you are reluctant to subsume Condemn off, then i would recommend using Magus lockdown to group enemies as an operator arcane.
Even with condemn we still have a giant source of shield income with the [Rakta Dark Dagger] which will generate shields when you damage enemies that have radiation procs on them, with a couple swings we are at capped overshields.
The [Rakta Dark Dagger] will only regenerate shield if you currently have even the slightest amount of shield to build on, it cannot regenerate from 0, to give this a headstart, [Augur Reach] is being used to create oportunities for slight shield regeneration.
our shield gating is enough to make any amount of damage useless before us paired with [Rolling Guard], but toxic damage will ignore our shields and often enough be our demise, penance lifesteal is great if the toxic damage is minimal but at higher levels in SP will oneshot no matter what; [Rolling Guard], Covenant and the panzer vulpaphyla are our fallbacks for situations like these but even so, toxic clouds should always be avoided.

Headshots/Crits:
[Harrow] does three things particularly well: headshots, crits and shielding, both Thurible and Covenant are boosted by headshots to get the best of them but are still viable without such accuracy.
While headshots would amplify the natural benefits of [Harrow], I will personally not be using it as the focal point of my build seeing as I plan on using melee weapons as my primary source of damage.
arcane avenger is being used as an arcane to gain 45% flat critical chance, just an all around good time :)

Infinite energy:
the thing [Harrow] is most notorious for is his immense energy regeneration, giving us access to more energy than we could ever know what to do with.
paired with headshots, the energy regenerated from this ability is quadrupled which is just a nice little bonus.
Since we have access to a limitless pool of energy, our abilities Ensnare, Penance and Covenant can be used as often as needed.
Magnetic procs aren't often a problem to us if the Penance buff is active but if caught off-guard with it no active, magnetic procs will completely destroy the energy economy which is hard to come back from, Arcane nullifier is just a [Safeguard] against these annoying situations.
If you are confident that you can maintain your energy economy then I would recommend either Arcane aegis for additional defensive power or Arcane strike for better DPS.

ARSENAL:
(I should mention that the weapons below in the brackets are the weapons I personally use, they are NOT OPTIMAL but are good enough for me, use whatever you like)

Primary: (https://overframe.gg/build/340833/argonak/harrow-rakta-amalgam/)

Secondary: (https://overframe.gg/build/350906/epitaph/primer/)
I know the [Epitaph] is a little bit of a braindead pick but there is a reason it is always picked, it is an amazing primer with guaranteed cold procs and super high status chance to apply things like, viral, radiation, innate blast, slash, impact and puncture all of which are in my build.

Melee: (https://overframe.gg/build/340684/rakta-dark-dagger/harrows-lifefore/)
Used for shield regeneration and gas nuking

Companion: (https://overframe.gg/build/320421/panzer-vulpaphyla/cyst-kitty/)
Panzer Vulpaphyla with synth fiber and undying mods.

Focus-school: Personal preference
(Naramon), I use this school because I am a big stupid idiot that cannot rely on himself to just keep the combo counter alive even with two dexterity arcanes.
I would recommend something like Unairu or Vazarin if you aren't as stupid as me.