Great Ones

The Great Ones are group of extremely powerful, multi-dimensional beings that can exist across several planes of existence. They have often been described as gods, and play a mysterious yet crucial role in the plot, as well as the overall lore. The Great Ones are not of this world, they are beings that reside on a higher plane than humanity.
There are, seemingly, two main categories of Great Ones. The first category is a Kin. The Kin are human beings that have been graced by eldritch knowledge, through contact with the Great Ones. They typically have tremendous power and abilities that can be considered to be "god-like".
The Second category would be the "true" Great Ones. Great ones themselves are unknown beings that are impossible to explain and comprehend through human thought. They are supernatural beings with incredible strength and stamina. They can be perceived by only those with the highest of Acuity, and can be described as having both demonic and godly appearances. Not much is known about these entities, but what is known is that they exist, they have desires and motives, and they are evolved way past human capabilities.

Lore

The Healing Church has pursued a strange goal for a long, long time; a goal that has been hidden from all but the highest of rank among them which is to summon or harness the power of the Great Ones. The Great Ones are not of this world, but powerful enough to be seen as gods. Moreover, Great Ones are Eldritch beings that reside on a higher plane than humanity. And this scared those who have found the truth.
Scholars of Argynvostholt revered the Great Ones, these beings who, either directly or indirectly, caused The Scourge. Deep beneath Barovia resides a labyrinth. Once thought lost to time, pathways leading into the tombs were either discovered or created. At one such entrance was the abandoned fortress of Argynvostholt. Here men were sent into the labyrinth and an academy was built from the husk of the fort to understand the strange discoveries inside, generally called the Eldritch Truth. The truth is a terrible thing, slowly breaking the mind of anyone who delves too deep into the underbelly of Barovia. It is rumored that the awful things has happened here, and as a result, the church has closed off not only the academy, but the entire forest.
Whether or not the Great Ones are actually gods or just higher levels of beings is inconsequential, the question itself is entirely academic. The important thing is: They exist. They have an influence on the world. They appear to be ageless, but they can be killed. Their powers are strange things, often involving teleportation or manipulation of energy, or things that people of the human world cannot do. Even perceiving the Great Ones properly requires great amounts of Acuity.
The plague was used as an outlet by the Great Ones as an attempt to find a surrogate for their lost children. As evidenced in description of each One Third of Umbilical Cord, this process involved the Paleblood Moon and an attempt to foster a new child for a Great One that lost their own. In the world of Bloodborne, babies that are treated as “special” in one way or the other are offered as lures to the Great Ones. When it comes to living creatures, the stronger or more advanced you are, the fewer offspring you produce in your life. The Great Ones have all lost their children because of their positions, and as a result, they're attracted to these special babies. The babies are one way of calling them.

Great Ones

Listed below are some known Great Ones.

Yellow King Yog- The Great Pain The Mother
V Dreamer: Dreams (The wanderer), Cthulhu ish. Has a twin that is nightmares.
V King in Yellow: Decadence, music
V Rhovna/ Previous Entity: Power and Blood
Nylarlethotep: Controlled Chaos???
Azathoth: Everything/Chaos
Shub: Fertility, Hunger
Spider girl: Expansion
Yogsothoth: Time
Cthulhu: Herald of Change
Vinerva: Benevolence/malevolence?
Malach/Kyrious: Technology
The emporer: Justice
Fear/ emotion
Secrets
Pain

"Every Great One loses its child, and then yearns for a surrogate, and Oedon, the formless Great One, is no different. To think, it was corrupted blood that began this eldritch liaison."