Mago Myth info (from Wikipedia)

Cosmology
Korean creation-mythology[1], or cosmology has many variations depending on the source, but can be generally separated into one of the following three categories: the first, totemic/shamanistic creation mythology, the second Taoistic cosmology, and the third, Buddhist-influenced cosmology. These first two are commonly referred to as pre-Buddhist cosmologies)

Totemic/Shamanistic cosmology
The totemic and shamanistic traditions are perhaps the most indigenous (i.e. "Korean") of the pre-literate cosmologies in Korea and involve a great deal of reference to local geography, such as mountains, rivers, etc. Ancient Korean totemic and shamanistic legends constitute a part of the larger unwritten oral literature which focused on the local Mudang (shaman). The Mudang acted both as a story-teller and a shaman, and usually the legends seemed to involve an attempt to justify the powers of the Mudang or to explain the origin of a certain clan.
Also known as the Mago-Mythology 마고신화(麻姑神話), this is actually one of the lesser-known Korean cosmologies due in part to the rising influence of Buddhism and taoism around this period, as well as the imposition of a patriarchal system which desisted the heavily goddess-oriented nature of the legend. The first mention of this cosmology appears to be the Budoji (부도지), written in 1953.

The creation of the World
At the beginning the world did not exist. A deity named Yul-ryeo 율려(律呂) and a goddess named Mago 마고(麻姑) appeared . Yul-ryeo then died. Mago in turn gave birth to two goddesses: Gung-hee 궁희(穹姬) and So-hee 소희(巢姬). They in turn each gave birth to two Men of Heaven 천인(天人) and two Women of Heaven 천녀(天女).
After the appearance of the Heavenly People, Yul-ryeo 율려 is revived and through her re-birth heaven, earth, and the oceans were created, along with Chi (soul) 기(氣), fire 불(火), water 물(水), and earth 흙(土). These four elements in turn mixed and became herbs and plants, birds and animals.
Mago 마고(麻姑) decides to stay with Yul-ryeo, whose body had now become the world, and the Heavenly People ruled all living things from their heavenly fortress named Magoseong 마고성(麻姑城) in honor of the goddess.
[edit]The Coming of Humankind
There were four Heavenly Men guarding each cardinal direction of the fortress, and they were Cheong-gung 청궁(靑穹), Hwang-gung 황궁(黃穹) who were children of Gunghwee, and Hukso 흑소(黑巢), Baekso 백소(白巢)who were children of Sohwee. They in turn married the four Heavenly Women, and gave birth to twelve children, who would become the ancestors of the humans.
These ancestors were pure and were have said to drink from Earth's Milk 지유(地乳), which came from a spring inside the castle. They could speak without making sounds, and act without seeing and never died. Thus they lived for ten thousand years undisturbed.
Then there came a time when the number of people became too large. There was not enough of Earth's Milk (or "Jiyu") to go around for everyone. Because of this, a man from the line of Baekso 백소(白巢) by the name of Jiso 지소(支巢) decided to cede his meal of Earth's Milk five times to his neighbours (other versions say that he waited in line but the line was so long he never got his turn). Eventually his hunger grew intolerable, and deciding to kill himself he headed towards a cliff, where he saw a grape vine growing in the edges. Unable to suppress his hunger, he ate the grapes and immediately acquired the five tastes of sourness, bitterness, spiciness, sweetness, and saltiness. This is known as the Incident of the Five Tastes (오미의 변).
Jiso 지소(支巢) returned to his people and told them of his discovery. Soon however, those who ate from these grapes began to grow teeth. From the teeth spewed a saliva that turned into venom. This was because they had eaten another living thing in order to stay alive.
Soon they were able to see, but were no longer able to hear the heavens. Their skin became coarse, their feet heavy, and they were no longer pure. They gave birth to many animal-resembling children and their lifespans began to shrink.
There eventually came a point when the people of Magosung 마고성(麻姑城) began blaming Jiso (지소) for the transformation, and he along with his family and all those who had eaten the grapes were forced to leave Magosung 마고성(麻姑城).
As the line of Jiso was leaving, however, Hwang-gung (황궁:黃穹, one of the four guardians and a direct ancestor of the Korean people) tried to encourage them by saying that if they could recover their pure nature, they would be free of their misery.
Upon hearing this, the people became convinced that the only way to become pure once more was to drink from Earth's Milk again. They then stormed the castle and overwhelmed it, razing the fortress to its foundations in order to reveal the source of the spring that had given them Earth's Milk. The spring, however, began to flow in all directions and thereafter the milk turned into inedible earth, leaving not only the original perpetrators but all the former inhabitants of the now destroyed castle to starve.
Soon thereafter there ensued a massive famine, and everyone was reduced to devouring not only grapes, but all sorts of plants and even animals in an attempt to satiate their hunger. Of them only Hwang-gung 황궁(黃穹) came forth to Mago 마고(麻姑) and begged her for forgiveness. He swore he would not rest until mankind could recover its pure nature. From her he obtained the Three Heavenly Heirlooms, and great knowledge. He then called together all the people of the earth, taught them agriculture, and gave each clan leader a Heavenly Heirloom and then sent them off in different directions to people the earth.

The Settling of the World
Cheong-gung 청궁(靑穹) went to the East, where he established China.
Baekso 백소(白巢) and his people moved to the West and became the people of Europe and the Middle East.
Hukso 흑소(黑巢) moved to the South, into the region that is now India and Southeast Asia.
[edit]The Establishment of Korea
Hwang-gung 황궁(黃穹) took three thousand followers and they alone went to the harsh North, to a place called Chonsanju 천산주(天山洲), meaning "land of the heavenly mountain" where the land was cold and dangerous. He had done this on purpose, because he wanted to be purified once more. Upon arrival, Hwang-gung 황궁(黃穹) signed an oath swearing that he would recover his purity.
Hwang-gung 황궁(黃穹) ruled for a thousand years, using the Heavenly Heirloom, which granted him power over fire and the sun. Hwang-gung eventually achieved his goal of self-purification. To his oldest son Yuin 유인(有因) he gave the Heavenly Heirloom as a sign of his right to govern the kingdom, whereas to his two younger sons he gave the responsibility of governing over a province each. He then departed to the Heavenly Mountain 천산(天山) where he became a stone that could speak Yul-ryeo's message, constantly reminding men of their path to innocence.
Yuin 유인(有因) ruled for another thousand years. Using the Heavenly Heirloom, he taught his people how to tame fire and cook food. He later left for the Heavenly Mountain as well and gave the heirloom to his a son by the name of Han-in 한인(桓因) [sometimes pronounced "Hwanin" 환인]. Han-in 한인(桓因) was the last of the heavenly rulers, who used the power of the Heirloom to bring abundant sunlight and good weather. Under the three thousand years of peaceful reign since Hwang-gung 황궁(黃穹), the people eventually lost their animal-like appearance and slowly began recovering their image.

Demystifying the Myth
Han-in 한인(桓因) later established a kingdom in Lake Baikal which he named Hwan-guk 환국(桓國), a proto-Joseon nation, from which the later Emperors of Ancient Joseon were said to have emerged. It seems that some of the similarities between the Dangun legend and the Mago legend (including the Three Heavenly Heirlooms, or the three thousand servants) might be because the Dangun legend borrows from the earlier Mago legend.
It seems that the original pronunciation of Hwan-guk 환국(桓國) was closer to "Han-guk" 한국 (as in "Han-in" 한인:桓因), which is the name South Koreans use today to refer to their country. Han-in also goes by different names, including Ahn Pa-kyeon 안파견(安巴堅), and Chonjae Han-in 천제한인(天帝桓因), meaning "Han-in Emperor of Heaven."
The Silla scholar Park Che-sang (박제상), mentions this myth as being much older than the better-known Dangun mythology. It is claimed that Hwanguk collapsed sometime around 3,898 BCE (Ancient Joseon's legendary founding date is 2,333 BCE), whereas it is said to have been established somewhere near the 1st century BCE.