When Pangu created the world, many living beings appeared in the world. The spiritual beings that grew out of Pangu's body after his death were scattered around the world. The gods of later generations classified these as the Classic of Mountains and Seas.
However, there are still mythical beasts that are unwilling to give in and want to do whatever they want in this world. In the end, the Emperor of Heaven could not bear it anymore and made a deal with the gods who violated the rules of heaven, so Jue was born in the world.