INTRODUCTION

This is a steel path endurance survival looting focused build using [Pilfering Swarm] to generate additional loot and oxygen, Tempest Barrage to deal AOE DPS, [Viral Tempest] augment to apply AOE viral procs, Breach surge to deal additional ability DPS as well as blinding eximus through overguard and finally Plunder which applies a corrosive damage boost to both Breach Surge and Tempest Barrage.

If you don't want any extra loot, simply swap [Pilfering Swarm] out for [Stretch].

Survivability Options:
1. Casual Tanking: This is viable for non SP and early base SP eg first few hundred levels or 1 hour survival etc. Simply swap [Catalyzing Shields] for [Adaptation] and [Augur Reach] for [Umbral Vitality] (OR just swap Molt Augmented for Arcane Blessing).

2. Shield Gating: With [Catalyzing Shields], we need [Brief Respite] + at least THREE augur mod spread over the frame, secondary or sentinel pistol to fully reset shield gate (to gain max 1.33s gate) with a single cast of Tidal Surge or Breach Surge. If you don't want to run all three augur mods, just running 2 augur mods will still give u almost 1.3s which is good enough.

Alternate Builds
For a nearly fully AFK looting gameplay: https://overframe.gg/build/311460/
Speedrun : https://overframe.gg/build/541107/

PLAYSTYLE

1. Find an area to camp in and cast tentacle swarm, ideally having one or two chokepoints.
2. Cast 3 when there are a decent number of enemies nearby, eg trapped in your tentacles
3. Spam 1 on a chokepoint to deal ability DPS, strip armor and apply viral procs in a fixed 10m AOE. You can infinitely stack 1 in the same area.
4. Cast 2 periodically to stun eximus, refresh shield gate and generate breach surge sparks which are much more effective against fully stripped enemies.

BUILD SPECIFICS

Duration
Duration is needed for Tempest Barrage, Plunder and Tentacle Swarm. [Primed Continuity] gives 155% duration.

Efficiency
Should keep neutral or positive for Tempest Barrage + Breach Surge spam, although 100 efficiency allows full shield gate from a single cast of Breach Surge. [Pilfering Swarm] improves energy orb drops. If you find energy is an issue particularly if you don't own Energize, consider adding other tools like Zenurik, [Dethcube] with [Energy Generator], Emergence Dissipate or simply [Equilibrium] over [Primed Flow].

Range
Higher range is preferred for Tempest Barrage and Breach Surge, although note that Tempest barrages initial radius is FIXED at 10m, while only the impact AOE scales with range. This means range is not AS important for tempest barrage as it seems, particularly if enemies are bunched into tentacles so AOE damage overlaps already. Plunder has a decent base range so it doesnt need a huge range boost. Unfortunately, high range is actively detrimental for tentacle swarm due to its high base radius and enemy capture limit. With 200+ range, you may find tentacles grabbing and trapping enemies outside of your current area which then prevents additional tentacles spawning on new enemies actively coming into your area. For this reason, i'd keep range between 100 to 175 depending on the map and whether you actually want to loot or not. If you want to just KILL and CROWD CONTROL enemies (eg circuit), you can make your range 175+. If you want to actually loot efficiently, keep you range around 100-130.

Strength
Strength is used to boost the damage of Tempest Barrage and multiplier of Breach Surge. The boosts from Plunder are a bit less important, since armor isn't important for a shield gate build, and corrosive bonus damage can be actively detrimental to status weighting on certain weapons (e.g. beams like [Ocucor], [Kuva Nukor] etc), since it lowers their heat weighting which is what deals the majority of status DPS.

Aura
[Brief Respite] is mandatory for the shield gating setup.
If not shield gating, swap for anything else eg [Growing Power], [Enemy Radar].
[Corrosive Projection] is NOT useful, as it is multiplicative with corrosive status and does NOT reduce the number of corrosive procs required to full strip.

Exilus
[Primed Sure Footed] to prevent knockdowns either from enemies or your AOE weapons.
Alternatives include [Handspring] or [Power Drift].

Flexible Slots
[Viral Tempest]: Optional since it only provides viral procs which u can simply apply manually if using guns like [Ocucor]. Can swap this out for [Streamline], Stretch, Augur Message.

Catalyzing Shields: Can swap this out for Rolling Guard if you are okay with generating less i-frames per ability cast (115 shield = about 0.7s) but at the benefit of having status cleanse and more i-frames on cooldown, or just [Adaptation] if you prefer to lazy tank for lower level missions.

[Rousing Plunder]: Optional augment that only boosts armor and corrosive dmg bonus from 3, which is already in the base ability, and adds some healing. Could be okay to use in a tank build, but not useful for endurance.

HELMINTH OPTIONS

Either subsume over 2 (for relatively stationary missions) or over 4 (on more mobile missions where you won't be looting in one spot).
I generally use a separate speedrun build subsuming over 4 for mobile missions.
1. Breach Surge - this stuns eximus units through overguard, receives a corrosive dmg bonus from Plunder (which double dips as Plunder also applies to your weapon and tempest barrage) and is particularly effective as ability DPS on enemies stripped by Hydroid's passive.
2. Nourish - mainly useful for energy to fuel tempest barrage spam, without taking extra mod slots, but also applies viral damage to your weapons. This means Plunder + Nourish applies both Corrosive and Viral to you weapons and you can drop all elements on your weapon builds for extra crit/dmg mods.
3. Roar - boosts the damage of viral tempest and your weapons.

ARSENAL

Use pirate, aquatic or tentacle themed weapons for fun!
Ocucor - https://overframe.gg/build/483134/ocucor/surging-tendrils-ocucor-sentient-surge/. Currently one of the strongest weapons to use with Hydroid, as plunder applies corrosive and allows Ocucor to full strip for itself while dealing Viral Heat.

Torid - https://overframe.gg/build/472389/. Very strong beam weapon, currently one of the strongest primaries. Also amazing with [Hydroid] as it can self strip while dealing viral damage. Note use the PURE VIRAL variant listed in Torid guide when using with hydroid.

Kuva Zarr - https://overframe.gg/build/226265/kuva-zarr/kuva-zarr-viral-hunter-munitions-anti-grineer/. Good option since Tidal Impunity makes you immune to self-knockdown, and Kuva Zarr looks like a cannon from a pirate ship.

Kompressa - https://overframe.gg/build/475341/kompressa/kompressa-empowered-dps/

Harpak

Nami Skyla Prime

COMPANION

Nautilus with Cordon and Manifold Bond for infinite suction: https://overframe.gg/build/540870/nautilus/hydroid-arsenal-the-whirlpool-nautilus-grouping-priming-dps/

[Shade] or [Huras Kubrow] for invisibility while you spam Breach Surge and Tempest Barrage

Diriga with Arc Coil + Manifold Bond for free condition overload priming, while using Verglas and Duplex Bond for DPS: https://overframe.gg/build/541464/diriga/hydroids-arsenal-ultimate-jellyfish-priming-dps-orb-generation/