HEY YOU! YEAH YOU!! DO YOU LIKE BEING A DISGUSTING BALL OF PURE PLAGUE? YEAH WELL SO DO I!!!

This vile virulent vigilantly is a frame I fell so in love with I stopped myself from playing him for a time. My playstyle for him is activate Pulverize and cast Feast on the nearest enemies while rolling over the battlefield. Throw in a few Nourishes to keep the viral damage and energy bonus for yourself and allies. Add in the occasional Regurgitate to armor strip and deal some damage. I cast these abilities while inside the ball and forget that gunplay exists ... for a time. I will pop out of the ball when lots of overguard enemies or enemies with high Damage Reduction (that can't be eaten) show up. Luckily, his kit works well with both ball form and standard form.

Let's go down this list step by step:

Aura mod: Whatever you want! I don't think this build really gains from a specific aura. I recommend [Stand United] or [Physique] to give your squad some extra survivability. I currently just run [Energy Siphon] or [Dreamer's Bond] as I don't have any auras that would benefit this build.

Exilus: Look this build for me is about being in the ball as long as possible in this case [Catapult] is the only option since it gives you extra speed. However, I think you could modify this build to remove the ball form by just changing this mod. At which point I would subsume roar or a grouping ability over [Grendel]'s 3.

[Stretch] for extra range, [Vitality] to make [Grendel] super tanky, [Blind Rage] to maximize damage with Nourish energy is no issue, and [Catalyzing Shields] because [Grendel] has low enough shields this is the best way to male use of shield gates. [Archon Continuity] has a fun effect of adding corrosive procs to Grendal's toxin procs which are his 1 and 4. The 1 only toxin procs when releasing your gut and the 4 doesn't benefit a ton since it already full strips, however this is still an additional guaranteed proc.

That's a lot of augments! Yes it is! There would be more but Overframe is still missing a few mods including [Gastro] [Grendel]'s newest augment.

[Gourmand] is an easy one for me, a maximum of 2000 armor AND your 1 costs health instead? Sign me up! [Grendel] has two forms of healing with Nourish restoring about half your health pool and ball. Pulverize (ball) has a constant passive healing effect per second. This is a big deal because it has a base heal of 200 per second! Ball certainly won't make you immortal but it can feel like it.

[Hearty Nourishment] is a good replacement to [Rolling Guard] that can be triggered without rolling. Or while literally rolling as the ball.

[Archon Intensify] is the last mod to discuss. With Nourish you'll find yourself easily keeping the additional +30% strength going. However, I would rather place [Gastro] in this slot. [Gastro] turns Regurgitate into a powerful damage tool as it adds gas damage. Gas damage? Powerful? Yes! The 4 will hit 3 times total with the augment dealing toxin, corrosive, and gas! If nourish is active it can also deal viral. I think that makes [Gastro] worth sacrificing the additional strength for.

Arcanes!! The website lacks the 1999 arcanes currently so the build shows what I would use pre 1999. Molt Augmented is an easy 60% strength. With 1999 arcanes I would replace this with Arcane Bellicose as it is that full 60% at mission start. The second slot I would use Arcane Battery as it scales off of all armor even the gut armor. So with a full gut you'd be rocking an additional 870 energy (if my math is right). Alternatively you could run both strength arcanes for an easy +120% strength.

Archon Shards? This is where we get to theory crafting while the rest has been (mostly) practical build crafting.
You could run 5 green shards with +10/15% ability damage on enemies under corrosive status since you are guaranteed a few corrosive procs. The wiki says this bonus is multiplicative to other ability damage sources. The green shards can also enhance your toxin status damage instead. Reds can also give a flat increase to your strength but the amount of strength already in the build makes me question how effective that would be.

If you plan on running around rather than rolling I'd recommend a yellow shard or two for casting speed. While rolling you have no casting animations and are gaining constant health so there's no real advantage to casting speed in that situation.