One Being

The One Being is preternatural entity and avatar of Azathoth that is the progenitor of the many Realms in the MK Universe.

Overview
The One Being's disembodied consciousness seeks to reunite all the realms in order to make itself whole again. It is implied that it has acted through beings such as Onaga and Shao Kahn, and is responsible for their attempts to merge all realms, particularly Earthrealm, into Outworld.

According to the rumors of Chaosrealmers and Netherrealmers, all of existence is only dreams of the One Being since his consciousness was shattered into what became the Realms. It is also stated that the Elder Gods' tendency to not directly interfere in the affairs of the realms is often due to fear of waking the One Being. It is also revealed that the Blood Daggers have all tasted the blood of the One Being and its essence lives within them, serving as the source of the daggers' Blood Magik.

Powers and Abilities
From the fact that it fed off of the essences of the Elder Gods, it could be concluded that the One Being holds the powers of each one of the Elder Gods, giving it nigh-omnipotence. It could also be concluded that it has control over time/space, reality, and all lives within the realms.

It has also influenced powerful individuals, such as Onaga, Shao Kahn and quite possibly Shinnok; into absorbing all realms (and their denizens), as a means of making itself whole again.

Ancient Legend
According to ancient legend, in the beginning of time, there only existed the One Being and the Elder Gods. The One Being fed on the essences of the Elder Gods, but eventually, the Elder Gods defeated the One Being, and, in efforts to weaken the One Being's near-infinite power, the Elder Gods separated the One Being's consciousness into the realms and created six Kamidogu, which held the essence of the One Being.

The legend decrees that if one were to obtain all six Kamidogu with the Amulet of Shinnok, he or she would be granted ultimate power.

Alternate Timelines
In one timeline, Shao Kahn is hinted at being under the influence of the One Being as he stands atop the Pyramid of Argus, prepared to bring about Armageddon and destroy the realms. This event is hastened to the final events of Outworld's, when Shao Kahn has almost merged Earthrealm with Outworld, and at the same time he is ending all things in existence. However, the Elder Gods intervene and destroy Shao Kahn, thereby halting whatever plans the One Being may have had.

In one timeline where the fallen Elder God Shinnok succeeds in remerging all the realms to reawaken the One Being, allowing it to destroy all of reality upon the One Being's revival and devoured the Elder Gods as his vengeance comes full circle.

Myths and Legends
Although the event of Onaga's resurrection would seem to hint that the One Being would be the final enemy, this was later proven false, as the Fire Elemental Blaze. The One Being is only mentioned, once in a passing statement about the kombatants "tapping into the power that make the realms", which may or may not refer to the One Being, and more directly by name with the personal story of Kai.

Despite the fact that Greater Elder Gods are parent-like figures to the Elder Gods as Kronika was to Shinnok and Cetrion, the One Being can be considered a primordial being as Cetrion says "We all are children of the One Being, As are all gods of the realms".

Equivalents
The One Being may be based on Khaos from Greek Mythology "the first living being from which everything was born" as Cetrion states that they are children of the One Being. The One Being's purpose in the Mortal Kombat mythos is incredibly similar to that of the twisted cosmic deity Azathoth in the Lovecraftian mythos.

Trivia

 * According to Jade, Jade mentions that some Outworlders pray/hold faith in the One Being whose religious aspect may have influenced the Edenian warriors to pray to him as well.
 * A interaction with Cetrion had her stating that they are children of the One Being.
 * Jade references the One Being as the God before Gods.
 * The One Being is referred to as "Yīgè Cúnzài" (一個存在 in Chinese) and "Hitotsu no Sonzai" (一つの存在 in Japanese).

Image Sources

 * (The One Being.jpg) The One Being cut from Mortal Kombat X
 * (Shinnok3.jpg) The One Being in Shinnok's ending from Mortal Kombat X
 * (Onaga the One Being.jpg) Onaga the Dragon King in his unseen ending, where he becomes the One Being from Mortal Kombat: Deception
 * (362miynvhot41.jpg) The One Being in the background behind the Elder Gods from Mortal Kombat Legends: Scorpion's Revenge