(3.10) Katmos’ Holy Zombie build (all game content for under 1 ex worth of gear, videos included)

Jewels that grant life. Non-abyss jewels are much cheaper than abyss ones (also, abyss jewels are not needed, because you don't need your minions to taunt or blind the enemy).
If you can, you can put some resistances on your jewels as well, to ease the pressure on the rest of the gear.
Each of those jewels shouldn't cost more than 1-2 chaos orbs.

1. Commander of darkness (you need to get the flesh and stone aura on you in order to benefit from the increased resistances)

what did you mean by this? FnS not count as aura and not trigger Commander Ascencion skill.

Please google this link:

https://pathofexile.gamepedia.com/Flesh_and_Stone

It clearly states that it affects you as well.

Well, the thing is - game do not increase my resistance wen i use this gem. No matter is it blood stance or sand stance.
Just look on this screenshots if you do not belive me.
https://imgur.com/a/7GUbBmN

ofcourse maby i doin something wrong. Is this stance must be linked with banner to work ?

You might want to use Metallic and Corroded with your Bound fossil. That way you do even less damage yourself so you don't have to worry too much about reflect. In which case you want to make sure you never quality it.

The Chieftains seems a bit naff to be honest, they very rarely seem to actually give me any charges, and it seems to be that they need to get up close and personal with stuff before they use their ability, which is tricky for them due to the zombies swarming around.

War banner trigger Commander of Darkness

Little suggesten:
Feeding Frenzy sup gives you a dmg buff on Cyclone from Spiritual Aid node maby replace Bloodlust sup with it.

Blood Magic Support on the Rais Spectre is it realy needed? Maby but War Banner in it and get on Left Claw Vaal Summon Skeletons with Increased Duration sup and Flesh Offering

Figured out what I was doing wrong, you absolutely need blood magic on the spectres, otherwise they will not cast the charges as they have a teeny tiny mana pool.

Correct. Chieftains absolutely need their blood magic and regeneration from the passive skill tree.

I saw Octavian0 playing aversion of this build. He should at least thank me!