The small world of Green Dwarfs was discovered by a family at the Thousand-island Lake by accident. But at that time, there were quite a number of powerful Green Dwarfs. The Old Man of Heaven Prison brought Bai Xi and some others to the small world and killed those powerful ones and took all the Mystical Materials in the small world.
The Old Man of Heaven Prison left it alone after that. The Bai Family would send someone in to pillage every now and then and clear out the powerful Green Dwarfs. After which, they would just leave the small world alone. Many people from the Thousand-island Lake had been here before. They were mostly here to train as there were few Mystical Materials left. Nobody dared to capture some Green Dwarfs to sell. Once discovered, the Bai Family would punish those severely.
Ming Yu had been here several times to train so he had a clear understanding of the small world of Green Dwarfs.