Zak’s Warhammer 40k universe(aka Zakhammer 40k) is my own version of Warhammer 40k universe, where it uses elements from bunch of different 40k editions and canons within single universe, this will highlight major things or differences that stands out about Zakhammer 40k universe:

here’s few rules in general:

-things like Blood Angels allied with Necrons are ignored as well things that doesn’t work for me in 40k universe(notably Grey Knights are easier to fall into Chaos than even Sisters of Battle) are also ignored

the Beginning/General:

• the year where C’Tan gods born into existence are 12.999.700.000 BC(300.000 years just after Big Bang)
• Old Ones are naturally evolved around 3 billion years since big bang 
• the solar system where Necrontyr came from are one of the Stars where C’Tan sniffs upon(this results in that Star emits Solar Flare that makes Necrontyr short lived) 
• Necrontyr’s original body prevents them from going Faster-than-Light with Inertialess drive when they left their troubled homeworld, but at least they invents Chronostasis field to survives generations of sub-light interstellar travel as well their spacecraft are utilizes Nanomachine-based regenerative material that’s better known as Necrodermis aka Living Metal to withstands rigors of Space Travel
• during Necrontyr’s first encounter with Old Ones, Necrontyr refuses to accept Old Ones as their new Math and Science teachers(which rewards Necrontyr Immortality that they wants and needs so badly if Necrontyr accepts Old Ones as their Math and Science teachers) due to Necrontyr’s dogmatic amount of Scientific Materialism 
• the FTL capable spacecraft that’s Necrontyr uses are exclusively unmanned ones(before Necrontyr undergoes species-wide transformation into Necrons) 
• Necrontyr’s Scientific Materialism are comes to play on making Necrodermis Warp-intolerant(this is what Old Ones(that using Proto-wraithbone constructs as their new bodies) exploit on shattering C’tan gods into C’Tan shards)
• Nightbringer are first C’Tan god that given physical bodies by Necrontyr with Necrodermis, it’s also coincidentally first C’tan god that later can remotely comprehend Warp(as a C’Tan shard) following it’s shattering by something that’s later known as Khaela Mensha Khaine 
• Szarekh the Silent King doesn’t shatters C’Tan gods by Necron Rebellion(at least through something other than his forces hacking Blackstone fortress) alone 
• Necron Overlord Ahmontekh blows up 5th rock from Sol named Maldek where one of it’s fragments later become Asteroid that wipe out dinosaurs of old earth 
• Mars in 40k are Earthlike Planet that turned into dead Red Planet during the War in Heaven(only later during Dark Age of Technology, become earthlike again by Human terraforming, and then become Red planet again during Age of Strife) by these fragments of Maldek 
• Eldar(created as Old Ones best psychic creations, where Old Ones leaders that uses Proto-wraithbone constructs as their new bodies are their Gods), Orks(created as ecosystem that combines the best elements of both Plant and Animal Kingdoms, spawned by Krork's dead), and Humans(created by biologically uplifting tree-beasts where their first psykers are used to continues Old Ones works following the extinction of Old ones themselves(in the hand of Void Dragon-led Necrons that seeds these Protohumans Pariah genes) with a Blackstone monolith) plus Tyranids(created in Andromeda Galaxy by fleeing Old ones where this causes the extinction of Old Ones and the rest of the life in Andromeda Galaxy, save for Zoats that flee to Milky Way galaxy) not to mention Zoats(biologically-uplifted Troodons that Old Ones evolves in Andromeda galaxy for either Old Ones assistants) are among old ones creations
• Certain C'Tan gods are shattered by Krork's Waaagh! Magic
• Just After wiping out Old ones that evolves apes into humans(with Blackstone monolith) in ancient Terra(and seeding them with Pariah genes), Mag’Ladroth got shattered into C’tan shards by a Blackstone Fortress(that’s driven by immortalized consciousness of Old Ones, better known as Eldar God Vaul) 
• one of the Old ones manages to Shatters Nyadra’zatha into C’Tan shards without using proto-Wraithbone body where he/she later reincarnate into a Perpetual Human that’s later known as Ollanius Pius 
• (general) Cryptids are exist in 40k where many of them are Extinct animals that time travels to either M3 or M41-42 with Naturally-occuring Warp gates that’s opened by Ley Line meeting points 
• Atlantis and Lemuria are Dark age Of Technology Terran cities that’s got temporally displaced to Pleistocene Earth 
• Noah’s Flood takes place during Pleistocene-Holocene border where Biblical Noah are Ollanius Pius’ persona there
• Outsider(aka Tsara’noga) are the only C’Tan gods that don’t shattered, at least in this 40k universe 
• (General) when Space Marines’ ribcage become armor plates, the part that used to be empty spaces in their ribcages will never be as thick as one used to be ribs themselves
• (general) Female Space Marine exists, as long as they’re no more of an Astartes than Kor Phaeron or Luther

Age of Terra:

• when Stone Age human psykers(better known as Shamans) sacrifices themselves to become God Emperor of Mankind, only one of them that’s don’t join the rest (and he’s artificially made Perpetual by Emperor himself and he’s must be none other than Malcador the Sigilite)
• Emperor’s mortal children makes up Human psykers that lives from Age of Terra to late Dark age of Technology(though psykers sometimes pops up from anyone unrelated to Emperor instead, and not all of Emperor’s mortal kids become Psykers) 
• when Emperor fought Shard of Void Dragon, he buried it on Mars inside a Master-crafted Tesseract vault(that runs on his warp magic powers) that’s known as Noctis Labyrinth 
• both Chainsaw Warrior game and Event Horizon movie take place in M3(latter is humanity’s first contact with Immaterium) 
• events in Event Horizon Movie did punish humanity from using FTL to even leaving solar system, rendering humanity to stick with Slower than Light interstellar travel 
• when Humanity first left Sol System, they first uses O’neill Cylinders
• Gellar Field are first discovered as byproduct of Antimatter detonation

the Dark Age of Technology:

• the very first Warp-based FTL method that humanity discovers are like this: taking Gellar field-generator equipped Spacecraft to naturally-occuring Black holes and use it as Wormholes(where the gellar field generator are serves as Wormhole key)
• Men of Golden are psykers whose powers are artificial enhancements instead of natural-born
• both Men of Stone and Men of Iron are Photonic-based Artificial intelligences(former are like traditional robots while latter are far more like living creatures with Carbon nanotubes for muscles and fibre optic for nerves) where their capabilities let them perfects String Theory and invents Border-space physics out of this(this allows Real World Pseudosciences(I’m not talking about Chemtrails or vaccines or anything about these here) to be scientifically proven to exist by the masses) 
• DAoT’s Jupiter and Matrioshka Brains(which used as CPUs for Dark Age of Technology’s AIs) also utilizes warp energy to communicate(just like 41st millennium’s Astropaths, except without human errors) and compute faster than light
• Warp Drive are first invented alongside anything that can artificially opens Black Holes
• Navigator(aka Homo Sapiens Navigo) are created to pilots Spacecraft that flies through the Warp as Normal Humans(psyker or not) with computerized aid can’t drive warpcraft through the Warp 
• Phase-Iron are invented just after following promotion of Psychic Powers and Warp Magics from Pseudoscience to Science 
• Felinids are one of Abhumans that debuts in the Dark Age of Technology 
• Emperor flies to Planet Moloch to get the data to forges the bodies and the souls of his posthuman sons via pact with Chaos Gods there. during his way to Planet Moloch, Emperor thanking a Blackstone fortress(presumably one that shatters Mag’Dalorth aka Void Dragon into C’Tan shards) 
• Warhammer Fantasy/Age Of Sigmar universe started out as simulated reality in a Matrioshka Brain(modelled after Dante’s inferno) where that Matrioshka Brain are later caught in the Eye of Terror during beginning of age of strife, later turning that simulated world into a Full-fledged reality(that no less tangible than Physical Worlds). at some point, Emperor of Mankind uploaded copy of himself into that where that copy will later become Sigmar 
• when Men of Iron rebels against mankind(as physical bodies for Warp entities), they become Chaos Androids(where surviving Chaos Androids are controlled by some Matrioshka brains near Galactic core, they’re later expunged by Imperium-Squat join operations, though lot of them are survives until Horus Heresy and Later eras), those warp-corrupted Matrioshka Brains are also spawns Chaos Leagues of Votann
• at least some of Men of Iron rebels against mankind from having their Matrioshka brains hacked by C’tan shard of Void Dragon
• the Psyker Epidemic that ends Dark age of Technology are caused by the most weak-willed people accessing the Warp

Age of Strife and Great Crusade:

• when Mars got de-terraformed to Red Planet again, the scientists that live there goes to the place where C’Tan shard of Void Dragon buried and they founds Cult Mechanicus where Void Dragon C’tan shard recreates everything from Dark Age of Technology that lost to whatever with everything in it’s power and strength
• the Squat has more psykers than any other Abhuman species(albeit not as much as Human(Baseline or Astartes) or Eldar ones) 
• Leagues of Votann was more Transhumanist Squat while Squat are less Transhumanist Leagues of Votann
• Asirnoth(which Ferrus Manus use to infuses his hands with) are Void Dragon’s C’Tan shard that stripped of it’s intellect and much of it’s powers 
• Valedictors and Rainbow Warrios being first founding chapters(whose primarchs are 2 missing Primarchs) 
• Valedictors’ primarch land on Feudal World that resemble feudal Japan and named Yamato Takeru While Rainbow Warriors’ primarch lands on Mesoamerican-style Feudal World where his front name are named after Aztec/Mayan/Incan deity while his surname are Latino/Hispanic 
• before their rediscovery by the Emperor, Yamato Takeru fought a Warp-infused C’Tan Shard that’s manifests as Yamata no Orochi and after defeating it, he advanced the technology levels of his adoptive world, by either using that captive C’Tan shard. while Rainbow Warriors’ primarch are undergoes Spiritual Journey so something resembles Mesoamerican underworld. 
• there’s race of Aquatic Carnivorous(albeit fish-eating) Abhumans that’s resemble Terran Dolphins whose psyker levels are closer to Eldar, this Abhuman species are survives just cuz they’re moved to Prospero only to be completely extinct by the time the Burning of Prospero happens 
• the Greed of Navigator families are comes to play on making Emperor refuses to tell anyone including even any of his sons about his Magnum Opus: Imperial Webway Project

Horus Heresy and the Age of the Imperium:

• the Blood Ravens are technically very first of the second founding Space Marine Chapter(that’s made by putting Loyalist Magnus’ shards into a vessel made from Rainbow Warriors’ DNA to create it’s first gene-seeds)
• the Detonation of Pharos Device allows Tyranids to go after Milky Way galaxy(after causing Class 10 extinction events across bunch of galaxies) 
• Primarch Yamato Takeru got lost in Time Vortex some time following Horus Heresy(where his dead body later used as Trazyn’s collection) where that time Vortex are caused by C’Tan shard known as Yamata no Orochi that Primarch uses as Trophy 
• Legio Cybernetica’s robots to Men of Iron are like comparing Feral animals to humans 
• Sisters of Battle draws their Faith powers from Emperor’s ability to give normal humans superpowers as well their own Faith 
• Horus’ Talon can neutralizes Perpetual’s regeneration from Warp Magic’s ability to destroy matter 
• the Tau Ethereal Caste are started out as Tau Hunters that become host for Iron Men’s Nanomachine cells(whose it’s fossilized deposits dissolved by water in T’au) during Medieval T’au 
• roughly around the time Adeptus Mechanicus gave up making Neoplasma reactors(from it’s prototypes made with their hands instead of Squats), Human-made Dyson spheres(and other stellar engines) that aren’t Squat-owned ones crumbles away from either gravitational pull of the very stars they envelopes as well their old ages(unless looted by Orks), this also make Imperial Gellar Field generators uses comatose Psykers instead of controlled Matter Annihillation
• the ultimate Source for Spyrer’s arsenals are Tau Earth Caste scientists working with Rogue Traders asked by Necronumdan nobilities to solve global warming(and so on) of their homeworld 
• Following Commissar Holt’s victory on Volistad’s war against Orks, the Orks resurfaced from it’s fungal infestation that defeated orks left behind(that deposited on Volistad’s ocean trenches) as Sea Orks, rendering Volistad eventually exterminatused(after the human characters in Final Liberation got evacuated) 
• General Sturnn and his Cadian 412th survives their Lorn V campaign from refusing last offers from Farseer Taldeer
• certain Leagues of Votann' ancestor cores spawn chaos androids
• Squats’ Nicoll-Dyson lasers saves them from their extinction by Tyranid splinter hive fleets, making Leagues of Votann wasn’t only Squat faction
• during the last days of 13th Black Crusade, Ursakar Creed and his men and women escaped with Warp Jump just before Abaddon drops Blackstone Fortress’ wreckage to Cadia(and destroying it)

the end of 40k Universe(and beyond):

• Commissar Sebastian Yarrick avoids fighting Demon Prince Angron
• during 6th sphere of Expansion, Tau forces took Yamato Takeru’s corpse from Trazyn’s Tomb World named Solemnace and studying it to make Gene-seeds for Gue’Vesa Space Marines(aka Gue’ron’vesa) 
• shortly after 6th sphere of expansion, Tau build a Matrioshka Brain that serves as new sept named Tau’va’shan(roughly translate into “Greater Good Heavens”) where it’s final resting place for a dead tau and this allows Tau to continue serving the Greater Good from beyond their graves 
• following the destruction of Commorragh by Ynnari, the Drukhari decides to make new Commorragh in the subterranean region of Traverse Town(in Kingdom Hearts universe) 
• Ynnari build a Matrioshka brain(that perhaps serves as last crone sword) to finish their job
• Tau’s army that employs Psykers are Farsight enclaves, not Mainstream Tau Empire(even then, the Psykers that any Tau’s factions employs are can’t be Tau members species-wise) 
• at some point following Plague Wars and Vigilus campaign, there’s civil war that splits Imperium to 2 factions: vanilla one, and one that considers Xenos as friends while Psykers just as human as everyone else 
• also, at some point during 42nd millennium, Belisarius Cawl teams up with Szarekh the Silent King that recently returns to Milky Way Galaxy to reactivates Blackstone Fortress in pariah Nexus
• Cawl then eventually back-stabbed by Szarekh, though he learned to make Servitors out of psychic blanks 
• around 1000 years after events in Eisenhorn novel series, Gregor Eisenhorn come back to life as his own soul housed in a Clone(Master-crafted Geneforge makes that) where this is what the incarnation of Gregor Ensenhorn that appeared in Ani-toonspiracy
• Tyranid made a new Hive Fleet that specializes in Eating mechanicals like Necrons after assimilating a forge world that specializes in nanorobotics 
• the Realm of Ultramar rebels against the rest of Imperium of Man and separate itself from the Imperium 
• Belisarius Cawl got arrested by Mechanicus of Mars and imprisoned on Mars, until the awakening of C’Tan shard of Void Dragon on Mars, where Cawl narrowly escapes there 
• Ynnead build a new Craftworld in the Orbit of Traverse Town where that craftworld combines the best elements of a bunch of Eldar’s major craftworlds 
• the Custodes that once known as Kitten(Emperor got TTS one) become first-hand witness of Emperor’s croaking in 996.M42 aka 41.996 AD where latter’s skeletal remains then become a vessel for Kingdom Hearts’ Heartless to destroys 40k universe for building Anunnaki’s Kingdom Hearts 
• both Grey Knights, Sisters of Silence, and Ordo Sinister psi-titans took the brunt of Anunaki’s Nanotech Heartless 
• by the time above happens, Hive Fleet Hydra, Ork roks, and Chaos forces converges on Sol system 
• people from different eras in 41st-42nd millennium lands on Traverse Town due to Warp’s temporal unpredictability 
• Genestealer cults land on Traverse Town as one of it’s criminal gangs
• Inquisitor Obiwan Sherlock Clousseau got Digimorphism from his augmentics(can transform into Assorted Digimons) at least some of horrors that Shadowkeepers kept are converted into Anunnaki’s Nanotech Heartless destroying 40k Universe
• Kaldor Draigo got killed off by Heartless after he sets up Timed Delay for Terminus Decree(to ensure most people from Holy Terra got evacuated to safety at the time of it's detonation)