Astartes in Mythology 40K FanFic

Escaped from the Backrooms is our Mc an Astartes Retributor, mowing down hordes of entities from the backrooms, he manages to escape the mono yellow wallpaper maze of insanity, via noclipping/stumbling into a void level in the backrooms... Finding himself in the very past of Earth aka Holy Terra of Greek Mythology he will have to battle his way through history and change fate as his power rivals that of gods. Meaning its a Warhammer 40K Transmigration and slight Isekai Fanfic of a Retributor (Space marine) into the Past. I do not own Warhammer 40K or its characters. I do not own any Space marine chapter mention in this Fanfic. I do not own the Backrooms. I also do not own the mythological characters as no one owns it. I also do not own the cover, it belongs to the creator of the Astartes CGI Film. I own the small slight OC's from time to time