This is one hell of a strong card, and a fantastic commander. The 4 colours lead to some much flexibility in terms of building it as a commander deck.
So how are we going to build it today, well we’re going to be building atraxa as a Phyrexian tribal deck, with a poison subtheme.

https://tappedout.net/mtg-decks/atraxa-grand-unifier-suggestions/?cb=1679488430

Tribal Matters (4-8)
Herald's Horn
Urza's Incubator
Skrelv's Hive
Phyrexian Swarmlord
Cryptic Gateway
Reflections of Littjara
Vanquisher's Banner

Poison Matters (6-10)
Ichor Rats
Inkmoth Nexus
Bilious Skulldweller
Blighted Agent
Pestilent Syphoner
Voidwing Hybrid
Thrummingbird
Bloated Contaminator
Evolution Sage
Tainted Observer
Inexorable Tide
Ajani, Sleeper Agent
Norn's Decree
Vishgraz, the Doomhive
Contaminant Grafter

Card Draw (8-10)
Experimental Augury
Prologue to Phyresis
Infectious Inquiry
Tezzeret's Gambit
Ezuri, Stalker of Spheres
Distorted Curiosity
Vraska, Betrayal's Sting
Ixhel, Scion of Atraxa
Ephemerate
Teleportation Circle
Conjurer's Close
Jin-Gitaxias, Core Augur

Ramp (10+)
Expand the Sphere
Myr Convert
Plague Myr
Farseek
Nature's Lore
Three Visits
Skyshroud Claim
Glistening Sphere
Arcane Signet
Chromatic Lantern
Vorinclex, Voice of Hunger

Interaction (8+)
Drown in Ichor
Vraska's Fall
Phyresis Outbreak
Phyrexian Rebirth
White Sun's Twilight
Cankerbloom
Viridian Corrupter
Path to Exile
Swords to Plowshares
Mortify
Putrefy
Damn
Supreme Verdict
Wrath of God
Fumigate

Protection (2-4)
Venerated Rotpriest
Skrelv, Defector Mite
Necrogen Communion
Lightning Greaves
Swiftfoot Boots

Recursion (2-4)
Unnatural Restoration
Glissa's Retriever
Sheoldred, Whispering One

Wincons
Sheoldred, the Apocalypse
Elesh Norn, Mother of Machines
Vorinclex, Monstrous Raider
Elesh Norn, Grand Cenobite
Brokers Ascendancy
Good-Fortune Unicorn
Cathars' Crusade
Triumph of the Hordes
Noxious Assault
Grafted Exoskeleton

Utility Lands
Karn's Bastion
Path of Ancestry
Secluded Courtyard
Unclaimed Territory

How to build a budget mana base Part One: https://youtu.be/fqT-JuV03_I

Intro Graphics by ptmotion
https://instagram.com/ptmotion?utm_medium=copy_link

Overdrive (By PraxI) by Diamond Ace | https://soundcloud.com/diamond-ace-music
Music promoted by https://www.free-stock-music.com
Creative Commons Attribution-ShareAlike 3.0 Unported
https://creativecommons.org/licenses/by-sa/3.0/deed.en_US