Previous 0 Forma Excalibur Guide: https://overframe.gg/build/478247/

This build is based on the concept that offense is the best defense. Generally, in Steel Path, enemies are stronger. Therefore, I am going to maximize the damage and efficiency of my Exalted Umbra Blade. Below is the Exalted blade I use:
Viral + Heat Exalted Umbra Blade: https://overframe.gg/build/473206/
Now that damage is at max, I build some durability. I don't use Radial [Howl] a lot, so I feel safe replacing it. It looks cool when I slide attack, but not it no longer blind enemies. My invulnerability on Steel Path largely depends on the use of [Adaptation], Slash Dash, and Radial Javelin. The Helminth ability I am using for additional survivability is Gloom. Gloom because if it isn't broken, don't fix it. Thanks to both [Furious Javelin] and Chromatic Blade this build just shreds all enemies in Steel Path like paper, and it still has excellent survivability at the 9999-level cap.

Enjoy and have fun Tenno.

You can ignore the unnecessary essay below. It's a long breakdown of this guide.

Explanation: Gloom slows enemy firing, movement, and attack by a certain amount. At level cap, this is a nice breathing room that provides a lot of survivability and comfort for the team if built for range and strength. I built for strength primarily since I am using a melee build with [Chromatic Blade], but I use [Augur Reach] for a bit of range. Also, Gloom gives lifesteal and I have [Adaptation] too, meaning that with [Exalted Blade]'s high damage and attack speed, I have become Immortal. Max efficiency is needed to run these channeling abilities without running out of energy. The energy orbs are enough to keep me sustained without problems. I would suggest you use Gloom on and off tactically because it can sometimes be Slow Nova kind of annoying.

Why use these mods? Other options? Archon Shards?

• Growing Power because it affects all our abilities and lets us achieve 272% needed for max Gloom Slow. Steel Charge works fine too.

• [Power Drift] for the bonus Strength and chance to resist knockdowns. [Chromatic Blade] needs 189% Ability Strength to achieve a 100% Status Chance. Alternatively, [Primed Sure Footed] if you are using Explosive weapons but you will need additional forma for it. Coaction Drift and Cunning Drift are okay too.

• Umbra trio mods are good stats, don't be weird and destroy Umbra polarities. If you are about to do that, then you should instead play regular Excalibur.

• [Fleeting Expertise] and [Primed Continuity] to obtain a very low channeling cost on both Gloom and [Exalted Blade]. I am using [Primed Continuity] instead of [Streamline] due to [Furious Javelin], if you lack it then I highly suggest you use [Streamline] instead as it provides a better energy economy. Also, Fleeting Expertise won't work with either Continuity or Streamline equipped first.

• [Adaptation] is the best defensive mod on Steel Path for [Excalibur]. Gloom turns me Immortal because it slows enemy actions and gives me life steals from Slash Dash, Radial Javelin, and [Exalted Blade] damage. Alternatively, you can use a [Rolling Guard] if you are going for endurance runs. Note: Shield Gating is not possible with a max efficiency build, so use Vazarin for its sling on endurance runs.

• [Furious Javelin] provides superior multiplicative damage instead of inferior additive damage such as [Blind Rage] or [Steel Charge]. Also, the Radial Javelin's 25m base range is still comfortable enough to play with, but if you want additional range on Gloom then you can use [Stretch] instead. The duration of the buff is only 15 seconds which is a tiny bit uncomfortable but it still provides a lot of damage making it worth it when I use it.

• [Chromatic Blade] is the best augment mod for Excalibur because it can clear everything DE considers to be content. I would suggest using Heat because it provides -50% Armor reduction and stuns for control. Electricity would work too, if you want more crowd control damage. If you don't have [Chromatic Blade], then [Surging Dash] is a good alternative, particularly if you're Naramon with [Ceramic Dagger] or [Magistar] Incarnons. Otherwise, [Furious Javelin] for everyone else who isn't a Naramon with melee Incarnons. [Stretch] for Range instead of Chromatic Blade would work well too if you want to focus on gunplay or your melee weapon over Exalted Blade.

• For archon shards, the best ones are the Crimson Melee Critical Damage followed by Ability Strength. Then Azure Energy Max, Health, and Armor are in that order. Amber shards are fine if you don't have anything else, I would suggest Energy Effectiveness, Casting Speed, or Parkour Velocity. I equip 5 melee critical shards to achieve the highest DPS possible, but if you want to be the more tanky then equip a mix of Health/Armor shards. Amber Casting Speed is a nice QOL, but not seriously needed since [Excalibur] is a melee fighter, not a spell caster. Eventually, you'll unlock Cavia once you complete the Whispers in the walls quest gaining the option to fuse archon shards. Once your rank 2 with Cavia, you can fuse shards into Violet Archon shards, Topaz shards, and Emeral shards. By then the best combo is 3 Violet shards in 25/37.5% critical damage which doubles if max energy is over 500 as well as 2 regular Emeral Archon shards to increase the max stacks of Corrosion to 14. With 14 stacks of corrosion, you can perform a full armor strip making it very good on bosses and any enemy, basically.

Arcane & Alternatives:

• The best arcane for Excalibur Umbra is Arcane Fury for an extra 180% damage on crit, and Molt Augmented for 60% Ability Strength after 250 kills.

• Offensive arcane alternatives are Arcane Avenger, Arcane Strike, Arcane Blade Charger, and Molt [Vigor]. I would highly suggest you use Arcane Strike or Arcane Avenger instead of Molt Augmented if you are not going to reach 250 kills in a mission.

• Defensive alternatives are Arcane Grace, Arcane [Guardian], Arcane Blessing, and Arcane Reaper. I have tried Arcane [Guardian], Arcane Blessing, and Arcane Reaper and they'll all perform very well. I don't have an R5 Arcane Grace to try, but I think it should be very good on Excalibur too.

• You can use an Arcane Energize, Arcane Nullifier, or something else if you lack energy. You should not lack energy, only if you're misusing it. I can leave both Gloom and [Exalted Blade] active for the entirety of the mission. If you subsumed his 1 or 3, then you can also slide attack during Exalted Blade to cast Radial Howl for half of the energy cost instead of pressing 2.

• For my operator, I use both Magus Elevate and Magus Lockdown, but anything goes.

These are the Helminth abilities I have used. I have ranked them in my personal opinion from best to worst:

1. Gloom: It's very easy to use, with moderate energy cost, a very powerful slow aura, and a very high life steal that affects teammates within 16m. I can regain my entire health after a single electrical beam, an instance of Slash Dash or Radial Javelin. Cons: The range is limited to 16 m which will always be less than the Radial Howl/Javelin 25m range no matter how I mod it. Gloom is constantly draining energy, making it largely dependent on energy.

2. Nourish: It has an average energy cost. It gives Viral damage when attacking or being attacked. It gives a Viral Damage buff, which is the best damage to have when paired with [Excalibur] Bleed damage, Unaraui, or any warframe with a complete armor strip. The energy multiplier allows me to spam abilities recklessly for shield gating, reduce efficiency, and put more strength mods. It buffs squad mates within 25m. Cons: No innate survivability.

3. [Xata]'s Whisper: It has a low energy cost and lasts for a long duration. It does everything Radial [Howl] can do to sentients but much better. It gives a Void damage buff, which is the best damage to have with Incarnon weapons as it leads to devasting damage. The status effect of Void, Bullet Attractor, looks very cool with [Exalted Blade] beams, making it spin for its duration. Cons: No innate survivability.

4. Fireblast: It is a cheap 100% armor strip that you can obtain fairly early into the game. With a full armor strip, we can kill everything on Steel Path easily. It also has an argument mod, [Healing Flame], that heals back health. It pairs very well with the Umbra trio mods, [Hunter Adrenaline], and [Adaptation]. Cons: Needs two casts from Fireblast to 100% Armor Strip.

5. Classics such as Eclipse, Roar, Well of Life, and Warcry are excellent options too. I prefer Warcry on [Excalibur], but you can use whatever you enjoy.

If you want to mod your Exalted Blade so it makes use of Archon Continuity, check this 2-forma 5⭐Nourish guide: https://overframe.gg/build/468118/

Other helminth guides are included below that are good too, but not as good as 5⭐Gloom and 5⭐Nourish:
4⭐2-forma Xata's Whisper Guide: https://overframe.gg/build/482491/
4⭐0-forma Fireblast Guide: https://overframe.gg/build/482468/
4⭐2- forma Warcry Guide: https://overframe.gg/build/482443/

I have put a lot of thought and time into this, thank you for reading so far :D

Math notes for myself:

Math: After turning both Gloom and Exalted Blade on. With 225 energy and 175%/190% efficiency, [Streamline], and [Fleeting Expertise], I can go on for 82 seconds without energy. With the 638 energy from [Primed Flow] and 130% efficiency, [Streamline], I can only go on for 31.5 seconds without energy. With Primed Flow, Primed Continuity, and Fleeting Expertise I can go for 98.9 seconds. With the 638 energy from Primed Flow, and 175/190% efficiency from both [Streamline] and [Fleeting Expertise], I can go for 246.5 seconds without energy. Overall, [Streamline] + [Fleeting Expertise] is best for 2 mod slots, but for 3 mod slots add [Primed Flow].