The Warioverse is a universe created by Unversed Entertainment, featuring content from them. The Warioverse was recently created, but the many stuff inside it ranges from old to new content. There are many timelines, and the universe is said to be connected to the Fantendoverse and Mysteriousverse, and therefore a number of other universes.
The universe was once a void of darkness, until the birth of The Sun, an all-knowing god. He spread his light, creating the first "Universe" of sorts. However, his all powerful light was observed by some of it's children, creating the first forms of darkness, Demons. These demons almost took over, but were stopped by a young creature(The Messenger).
Many years later, after The Sun's death, the Spirit Council decided to split the land into seperate universes for the safety of all. One ghost learned how to shift across the universes(GHOST SMILE). Intending to use the hero's powers, the shadow of the demon Mythic got close, but was defeated. As one final act of hatred, he accidentally shifted the entire universe over into the Fantendoverse (GHOST SMILE II).
However, one demon, a universe shifting demon with an unknown name was able to stay, excited to take up the opportunity to rule. Summoning those from across all multiverses into his game, he took up the name Mr. D. However, he was found out and beaten(Battle Theater). Fleeing to the Mysteriousverse, many heroes followed. The civilians left soon lost the concept of universe travelling, turning the heroes and villains of the past into a simple legend.
Many years later, the heroes were reincarnated. A villain born with the power of dimension travelling Dimentio soon set his sights on the souls of the worlds, making the reincarnated heroes unite once more(Silly Showdown). Sometime before this, in Prime Earth, in the near future, a goverment scientist was killed by a lone rodent(Rodent Story) . Although this halted the development of robotics on the planet, they later advanced when they contacted other worlds through Dimentio's hijinxs.
From here, with a bright future, the Warioverse split into many paths.