In late game, this build has 600+ hull (the health bar is literally longer than screen width), 60+ regen, 5+ plating, and 60%+ damage reduction, which is almost invincible. The damage is also busted, anything touches the serpent's body dies instantly.

Like if you are in a mine field, or surrounded by lots of Celestials and Hammerheads, the ship's hull doesn't even change much.

Beyond Wave 400, only these 4 enemies could possibly kill you, if you are very careless.

Must
Ataraxia
Hidden Power

Recommended
Dying Star (highly recommended, it kills rocks and small enemies)
Last Stand
Void Slice

Must
Adaptive Armor (whole tree)
Hull Strength (whole tree)
Kinetic Boost (only itself. Can also use Celestial Lance, regen is ususally higher than self damage, but Wild Mod choice is restricted)
Regeneration, Rapid Reconstruction (Regenerative Shields and Adrenal Module are optional)

Recommended
Improved Thrusters (for Blink)
Efficiency (no Gemini Protocol)
Candescence (no Corrosion)

Must
Bravado
Defiance
Evolutionary Niche

Any Wild Mod that levels up is great, because it buffs the Leviathan body. But don't pick them too early, especially Quantum Decoherence and Transmogrification, rerolls are extremely important.

Any Wild Mod that gives extra recursive mods is great, and it synergies well with Grandeur. Obsession is not very good. If you pick it late, not worth it. If you pick it early, you can't pick too many recursive mods, since max hull is extremely important. If you decide to use it, pick only a few very good recursive mods, and save the sp for Ataraxia (20).

Recommended
Chaotic Ambition
Discord (survive early game in Endless Mode)
Hypermetabolism (use at most 1)
Masochism (don't use too many)
Phantom Strike (seems good, but not necessary)
Rampage
Scorching Wake (survive early game in Endless Mode)
Winnow (extra banish)

In Draft Mode, it's straightfoward. Just skip Weapon and Shield. If you feel lucky, you don't even need to use any trick.

But in Endless Mode, you need to survive the early game. This build heavily rely on Wild Mods. And as we all know, Station Omega kills Leviathan.

Pick a handy weapon. I highly recommend Torrent, Vortex, Dart, Thermal Lance and Swords. The first 4 kills bosses and elites quickly without any upgrade. Swords reflect bullets, hits enemies behind shields, the damage is also decent.
Skip the shield.

Choose Research ship. It's almost impossible to get the build without Reserch ship's ability to banish. If there is no good mod choice, banish a mod. Don't use all the banishments on tier 1 mods early, because it makes Regression less effective. Hull and regen are 1st priority, Discord Orb is super good if you get it early, it makes up the weapon's short range.

After you kill Station Omega, pick mods and do banish mods normally. When you see Leviathan body, switch to it. At this stage, even with Annihilation on, it's difficult to die.

Keep at least 5 sp for Ataraxia. If there are good mods, just pick em, no need to wait 10 or 20.
But if you chose Evolutionary Niche (multiple times), Quantum Decoherence or Transmogrification early, and there is no good mod in the pool, you can save more sp. Wait until 10 / 20 spare sp, then pick some trash mods to see if there are better ones behind.

Celestial Lance is not bad, Dying Star is not necessary if you chose it. Normally, the self-damage is much lower than regen, you can slow down when you need heal.
The problem is, you can't pick too many Rampage mods, and rampage is super good.