Fabricating myths, starting with the creation of eight fictional ancient tribes

This book is also known as: I, the mastermind behind the scenes, deceived the entire planet Earth.
Having traveled to a parallel world on Earth, Wan Xingwang discovers that Earth's mythology is missing; there is no Classic of Mountains and Seas, no Investiture of the Gods, and no Norse gods.
Since that's the case, then I'll make up the myths of Earth!
Behind-the-scenes story, invincible story, incredibly satisfying, all extraordinary origins are created by the protagonist.