The World of Nightmares is a section of the afterlife meant specifically for souls that have no worth or value. In addition to those souls, Spirit Beasts commonly make their home in this world.
The World of Nightmares was not always the wasteland it once was. It was first created by the Spirit Beast known as the Birth Mother. The Birth Mother resents biology, so the entire world was made completely of metal, and its inhabbitants were metallic spirits. However, the Birth Mother grew curious of biology, and created the Spawning Pool. The Spawning Pool was a giant "pool" of genetic material of every kind of Spirit Beast and living being known in the world. This pool was literally a giant pool of DNA. With it, the Birth Mother created 2 other forms of life. The first one was the End Beast, a beast that would gain power by feeding on souls, and the Collective, a singular sludge with mind control abilities. However, the Birth Mother failed to realise her two creations were smarter then she anticipated. The End Beast and the Collective used the spawning pool to create a biological army to kill her. The End Beast then fought and defeated the Collective, absorbing it into himself. With this, he became the ruler of the World of Nightmares. The End Beast began to feast on souls and use the Spawning Pool to create more beasts, but the world was getting too big. He created the Black Cat to organize the souls for him. The landscape of the world changed from a metallic realm, to what everyone sees today. Through a battle between the End Beast and Amnesia, the Collective was accidently set free. The Collective spread incredibly fast, absorbing spirit beasts into itself and developing a "unity". The End Beast, and few other spirit beasts, such as Yamachi, survived the corruption, but the Collective mysteriously pulled back. The End Beast then retook its place as the ruler of the World of Nightmares. An encounter with Taro, Tiburan Momochi and Orr Tann, allowed the End Beast to become curious of humans. He created Emiko and sent her to find out as much as he could about the human world. However, he was alerted to the sudden return of the Birth Mother, who was reborn into the world, and she took control of much of the Nightmare World. Soon, the Collective returned as well, infecting the human world, and planning to take control of the Nightmare World as well. The Nightmare World is currently under a civil war between Birth Mother, End Beast and the Collective.
All of the noteworthy inhabitants of the World of Nightmares are spirit beasts, as the rest of them are spirits without worth, which are very commonly eaten by the End Beast.
End Beast- The End Beast is the ruler of most of the World of Nightmares. He commonly creates insects and other beings in his spare time, but commonly adresses more powerful prescences. The End Beast is actually a very curious creature, serving as a leader who commonly creates things for his own personal interest
The Collective- The Collective is actually many spirit beasts formed into one collective concious. The Collective refer to themselves as "we" and "us". The Collective believe that they are a part of the "Unity" and that all things must join them, so that the world may live in peace. The Collective have incredible mind powers, able to take control of most beings.
Birth Mother- The Birth Mother is the creator of the World of Nightmares. The Birth Mother hates all biology and prefers to use technology and steel. She thinks of herself as a God, and is actually good at playing God, making technological creatures more powerful then most people. She wants to return the World of Nightmares to what it once was.
Amnesia- The Amnesia is a very powerful brute monster with no concious other then to eat. It commonly calls humans from the real world so that it may devour them.
Black Cat- The Black Cat originally organized souls for the End Beast, but was taken control of by the Birth Mother.