We are born from the Infestation, which means we know best how to make it bleed
This build focuses on grouping enemies to make them easy to mark quickly with Blade Storm, and slice through them all at once with a heavy attack Zaw to regen your energy. High survivability is also provided by invisibility and armor. Use with my recommended loadout - [Mutalist Cernos], a [Plague Keewar] Zaw and [Panzer Vulpaphyla] for some beautiful synergy. Don't forget to buy the [Ash] Ichneumon skin to complete the infested theme ;)

[Ash] may seem a weak frame considering most of his abilities can be done better by other frames. His 1 has complete armor stripping and his 3 can [Reach] some INSANE damage, but both only deal with single targets. Enemies marked by Blade Storm are often killed by teammates before you can even activate the ability. And his invisibility, well, would be nice if [Loki] could share some duration.

But adding an enemy grouping ability like Larva can make up for Ash's main weaknesses, his lack of AoE damage and slow ability activation. Using weapons with high punch/[Follow Through] means you'll be slicing through the whole room at once. It also removes the need to mark enemies with Blade Storm, as they are already right in front of you, significantly speeding up the ability.

(none of this would be needed if DE would just buff [Ash] with more shurikens and made Blade Storm a FoV activated ability, but hey we're stuck with Helminth for now)

Forma Cost:

This build costs 1 Forma minimum, but can be increased to 3 for Primed/Umbral mods.

Playstyle:

Larva - Cast in the center of all enemies and then you have multiple choices for how you dispatch them. Drop a cloud of status on them with the [Mutalist Cernos], then one tap them all with a heavy attack to refill your energy. Or do a quick [Swipe] with Blade Storm to proc finisher Arcanes. Try to cast in open rooms to avoid getting enemies stuck against walls, as it won't be available for re-casting unless you kill all enemies it's attached to or it lasts for the full 14 second duration.

Smoke Screen - Even though the duration on this is lacking, invisibility is still the easiest way to avoid damage. Keep it cast as much as possible, energy shouldn't be a problem if you use my recommended loadout.

Teleport - Can open enemies to finishers, or be cast on enemies being killed by Blade Storm to join the animation, which provides you with a period of invulnerability if needed. Also a devent mobility ability with it's high range. But it is definitely his weakest.

Blade Storm - Cast when invisible for half the energy. Enemies grouped in Larva only need one quick [Swipe] of the mouse for them all to be marked. Damage is increased by your melee combo multiplier. If enemies are killed by the initial hit damage, not the subsequent bleed proc, then it counts as a finisher and will activate Arcane Ultimatum. This is easy to achieve so long as you keep your combo counter up and prime the enemies with status when you get to higher levels.

Mods Explanation:

AURA - Steel Charge - Extra melee damage is always postive, and gives an extra 4 capacity.

Continuity + Narrow Minded - Add duration for keeping Smoke Screen up.

Overextended + Stretch - Add range for Larva's grab radius.

Blind Range - Some strength for Blade Storm's damage.

Flow + Fleeting Expertise - Make sure you have enough energy for all the Blade Storm marks.

Vitality - Vitality on your frame keeps the doctor away.

EXILUS - Cunning Drift - Adds range for Larva. Can be substituted.

Arcanes:

Arcane Strike - The melee speed helps you increase your combo counter much faster. Unfortunately does not speed up Blade Storm unless you join in with Teleport.

Arcane Ultimatum - [Ash] is a very finisher centric frame. His teleport opens enemies to finishers, and Blade Storms inital hit damage counts as a finisher. This means you can have this Arcane constantly active. It gives an extra 4,410 EHP so is well worth it.

Operator:

Naramon

Power Spike - Allows a constant high combo counter to buff Blade Storm and a heavy attack melee.

Executing Dash + Surging Dash - Adds another guaranteed way to proc Arcane Ultimatum.

Void Stalker - Can top your crit off to give guaranteed red crits.

Magus Lockdown - Extra CC and holds enemies for easy finishers.

Magus Repair - At rank 3 this takes 5 seconds to heal 100% of your frame, which is the same time Void Stalker takes to [Reach] its max 50% crit. The 50% decays quickly so shouldn't be relied upon, but is nice to come out after healing with the extra power.

Substitutes/Extras:

• Primed/Umbral mods can be swapped for normal to reduce Forma cost.

• Steel Charge can be swapped with Swift Momentum for an extra buff to your heavy melee.

• Exilus can be swapped for anything. Primed Sure Footed or Handspring can prevent vulnerability from knockdown.

• Equip a decaying dragon key to reduce your shields. Shield gating gives you enough time to recast Smoke Screen and with reduced shields you will regain the gating faster.

Loadout:

Mutalist Cernos - Drops a cloud that procs status over an AoE. Shoot to where you are dropping Larva to prime all the enemies inside.

Plague Keewar Zaw - Use on grouped enemies in Larva to quickly max combo counter, then when in need of energy unleash a heavy attack. Scythes proc a forced bleed on heavy attacks, which is buffed by [Ash]'s passive. Exodia Brave does not [Regen] energy if enemies die to the bleed though, but this one shots most things anyway.

Panzer Vulpaphyla - This companion can heal you and prevent you from taking lethal damage over and over again. It's good to have a plan D, after invisibility and shield gating and armor. Also gives free viral stacks on enemies.

Enjoy the build, eLordyy