Mortal Kombat is absolutely crammed with lore, so much so that even die-hard fans of the long-running series can find it hard to keep up with the franchise's massive roster, multiple timelines and various seismic events. With necromancers, demons, two Sub Zeros, multiple four-armed warriors, Elder Gods, Titans and supernatural Kahns, Mortal Kombat can be as overwhelming to a novice as a classic Russian novel.
Mortal Kombat 11 finally introduced Kronika to the series, a figure so mighty that she is classified not as an Elder God but as a Titan, a race of beings that outmatch even the likes of Raiden and Fujin in terms of the power they are able to exert over the realms. Yet even Kronika and her ability to bend the arc of reality to her will (thanks to her control of time and space) doesn't come close to the universe's ultimate power ceiling. In search of that mysterious entity, fans should look to the strongest and most elusive figure in the entire series: the One Being.
The One Being is canonically the most powerful entity in Mortal Kombat. First mentioned in Mortal Kombat: Deception, the One Being is essentially the franchise's own imagining of a supreme being. Despite the series' evidently pantheistic lore, it is the One Being who sits atop the pile as the god among gods. Much like Marvel's One Above All or DC's the Presence, the One Being is an entity so vastly powerful and, at one point so omnipotent, that all beings in the universe were subject to its terrifying omnipotence.
After all, it was the One Being who essentially birthed the franchise's famous realms. At a time when only the One Being existed in conjunction with the Elder Gods, it was defeated by the Elder Gods by splitting the deities' power in an effort to dilute and diffuse its influence. In doing so, they created six Kamidogu, which were essentially ancient relics containing immeasurable power. Think of the Kamidogu as being akin to Marvel's Infinity Stones crossed with a Horcrux from Harry Potter or Sauron's Rings of Power in Lord of the Rings.
In doing this, the Elder Gods were successful in dividing up their nemesis' power and diffusing it across the realms so that it didn't exert so much control, somewhat assuaging their fears that such terrible power could exist in one soul-stealing entity. The Elder Gods' fear of the realms being merged comes primarily from the concern that doing so will reunify the One Being and threaten their very existence.
This isn't to say that the One Being doesn't still exert immense influence and control. Just as Sauron's ring holds sway over its bearers long after his physical demise, so too can Mortal Kombat's ultimate evil exert control over others so that they do its bidding. Most fan theorists think that Shao Kahn's attempts to merge the realms were a result of the One Being's pernicious influence, while others speculate that the arc of the entire series' lore is manufactured by this all-powerful presence pulling the strings in the shadows and using figures such as Shinnok as vessels for its power.
Whatever the case, the fact remains that startlingly little is known about the most powerful figure in the entirety of Mortal Kombat. Many speculate that the One Being might feature in an upcoming installment of the series. So far, the franchise's major villain has only been hinted at either by being mentioned by other characters or in non-canonical character endings. Only one actual image of the all-powerful deity exists, unlocked upon completion of Shinnok's tower ladder in Mortal Kombat X.
If and how the One Being will appear, however, is something only Ed Boon and perhaps a handful of others at NetherRealm Studios know. The franchise has been branching out recently, and the inclusion of Kronika indicates a desire to see the bounds of its lore stretched to their limits rather than merely retreading old stories or classic villains such as Shao Kahn, Onaga or Quan Chi. Since rebooting in 2009, it's felt like Mortal Kombat has been building toward some sort of seismic event, the stakes seemingly always increasing with each new installment.
In order for the One Being to return, it would likely need an event similar to that seen in Shinnok's tower ending, where the Elder Gods, as part of a "greater collective," are subsumed back into a singular entity after Shinnok merges the realms and "awakens" the threat feared by so many. This means that a storyline in which all realms are finally merged, something that has always been hinted at but never truly explored (Onaga's secret ending aside), could happen for the first time in Mortal Kombat's history.