The dedicated melee mastery for Scouts. I personally think it's gotten a bad rap and it is much better than you think. I will guide you on how you can get consistent N! wins.

Obligatory link to sylph's guide for basics.
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2714349654

2. Hellrunner.
3. Hellrunner.
4. Dash.
5. Executioner.
6. Assassinate.
7. Skilled.
8. Skilled.
9. Energy Leech.
10. Assassinate.
11. Executioner.
12. Executioner.
13. Energy Leech.
14. Energy Leech.
15. Assassinate.
16-18. Hellrunner/Dash.

Two levels of Hellrunner and Dash at start for repositioning and overall consistency, then mastery at level 6. With Executioner 1 and Assassinate 1, the Assassinate skill already has critical chance 100%, 200% if you are Stealthed.

Unless you got a very good AV2 machete in Callisto, 100% crit won't be enough to OHKO cryoreavers and kerberos, so two levels of Skilled for increased max energy and two stealth kills, then one level of Energy Leech.

With Assassinate 2, now your assassinate skill has critical chance 150% so focus on getting Executioner 3 to raise critical chance to 200% then max Energy Leech before getting Assassinate 3.

The rest of the skill points should be spent on defensive traits.

Recommended branches in order:

Rift: Poison Immunity will pay off in Io/Dante.

Mimir: Can craft AV2 machetes at MDF central but no guarantee you will get good perks with the limited number of multitools at this point. (Ambush 20/Hunter 20/Rush 20/Frenzy 20).

Mines: Very dangerous (don't rush the summon points because there is a good chance you will get swarmed), but a set of JS armor means that you can stop at Executioner 2 for 105% base crit and can spend the next skill point on Energy Leech 2.

Valhalla Terminal: Your armor will take heavy beatings so it is actually defensible to pick this option, and you get noticeably more experience after getting the 3 blue cards and shutting down Warden, which means your melee build comes online faster.

Avoid others.

Make sure to grab the free machete in the silver chest by the Europa L1 elevator if you don't have a melee weapon yet.

Asterius Habitat: At the end, you can craft AV2 machetes, but micromanaging the AH sentries can be painful in respawning difficulties.

Conamara Chaos Biolabs: Just avoid Hubris Labs #1.

Europa Dig Zone: The best option. Can craft AV2 machetes in Tyre Outpost and even use the multitools from the tech station to reroll perks if you need to.

Europa Ruins: Ancient mod and the Ancient speed relic are the biggest rewards. Probably won't have the most kills with melee for the AV3 melee amp.

Refueling Base: Not recommended. Even if you have a very good AV2 machete, this fight will be very energy intensive.

The Pit: Easy level.

Make sure to grab the Katana at Io L1 if you don't have a better weapon by now.

From experience, you actually will not have enough melee kills to get an AV3 Melee AMP at Shadow Halls or the Io Black Site so be aware of that.

Most of the time, you will be in Shadow Halls because you didn't get the red keycards or Io Black Site was not available.

Io Black Site is still a solid option because of the craftable AV3 katana.

The M. Mines can work if you are already poison resistant and there is a guaranteed AV3 katana at the end.

Avoid the CRI labs aka Hubris Labs #2.

If you are struggling, you can skip to the Io Warehouse/Infernal lock.

Dante Vestibule:

Kill any enemy with a melee weapon to open the portal to the Shatter Abyss, which is where you actually started. This is really important because you want the Soulstealer. I guess it is theoretically possible to win without it, but why take the risk.

The Shattered Abyss:

Normal reaver packs will be easy. Against archreavers, lure them one at a time to an isolated position then assassinate it, repeat.

Dante L2, Inferno, and L3-L4:

You should start killing everything with the Soulstealer to build up it's power. Don't bother assassinating guardians at start since it won't OHKO. Make sure you clear Dante Inferno just to feed Soulstealer kills.

Harbringer:

If you want to avoid the possible 100 damage at phase change from 1 to 2, finish phase 1 with a ranged weapon or grenades.

For amor, Meshed (power) is the most important perk. Bleed will lower your accuracy through pain and and deal a lot of damage over time if you are fighting against multiple enemies that can apply bleed. Standard Durable (bulk) and Swift (accuracy) fill out the rest.

7.62 Rifle: Speed-loader (bulk), Calibrate 1 (accuracy), auto-calibrate, and one wildcard.

Plasma Rifle: Speed-loader (bulk), and autocalibrate, and 2 wildcards.

Bladed weapons: Guard 10 (bulk) then Resilient (accuracy).

For AMPs, look for the general utility perks, with Energize (Until Energy Leech 2), Metabolic Boost, and Silent being the most important.

Don't worry about the max HP loss from Medusa since you will get it back with the Soulstealer.

Hoard multitools to repair amor in the late game. You can live with one ammo stack or two once your build gets going.

Keep a spare power mod pack in your inventory in case you find a Duramesh, Necrotic Armor, or an AV3 amor with the Silent perk in the end.

Due to frost guardians, I recommend keeping the frozen heart in general.

https://youtu.be/ZAmqJT-dm0U