Its beginner friendly version of my other build linked here:
https://overframe.gg/build/193639/nidus/absolute-chad-unkillable-steelpath-endurance-warlord-nidus/

It requires only 3 forma non of which are umbra if you just started grinding for that sweet steel essence, but is just as unkillable as the one linked above.

Lets go over picks that some might find controversial:

Steel Charge - mostly just for the bonus 4 capacity but its still nice to get that +60% melee dmg, swap it with anything else and you need to either drop overextended for stretch which is bad in my opinion or use umbra forma

Overextended - Its great to almost double parasitic link's range, that lets you be way more mobile and not just sit 20m tops from linked enemy.

Abundand Mutation - If you die back to back in less than 30 seconds then removing this mod wont help you much. You want to take it as it makes your abilities scale well into SP and negates any strength loss from overextended. You can swap this out with any augument you like or even save 1 forma and skip it entirely.

Adaptation - with this and his 3 you can stand still and take anything enemies can throw at you, even acolytes cant take your health down, with adaptation youre a tank, like a literal M1 Abrams 60 Tons Combat Tank

Rage - we pick [Rage] here 100% as its mod that everyone should have and its cheap if you dont, also the lower drain allows us to only spend 3 formas

Coaction Drift - its just that there are no good exilus mods for [Nidus], you can even drop them entirely and save one forma its up to you and what you like, for me its either this or enemy sense

When it comes to arcanes:

Arcane strike - i like to drop melee attack speed mods from my [Nikana Prime] to push more dmg, especially since berserker fury got changed and i just dont like using it in the builds

Arcane Guardian - great arcane for maxing survivability in the few second between parasitic links, more expensive option and also great pick is Arcane Grace, but due to rarity and/or price i chose to stick with [Guardian]

NOTE: IF YOU DONT HAVE ANY ARCANES YET YOU CAN SKIP THEM, THIS BUILD DOES NOT REQUIRE THEM TO WORK AS INTENDED.

Quick guide on how to use it:
1. Get into group of enemies
2. Cast larva
3. Spam virulence till you have 1 mutation stack
4. Cast parasitic link on any enemy
5. Congratulations, you are now unkillable and can repeat first 3 steps to stack mutation for giga dmg