.... I was bored, okay? And I love the Cosmic Entity so yeah, I decided to do this lol

WARNING: Contains season 13 spoilers, so don't read if you aren't caught up yet!

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Bibliographical information
Name - Cosmic Entity
(also Empty!Cas)
Species - Primordial Entity
Status - Alive
Occupation - Ruler of The Empty
Affiliation - The Empty

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The Cosmic Entity is a mysterious being who lives in and controls The Empty, a place of nothingness predating God, Death, and even The Darkness.

History
The entity controls the Empty and it explained to Castiel that the Empty existed before God or the Darkness. When angels and demons die, they go to the Empty where they eternally slumber, allowing the entity to do the same. If even one of its charges is awake, the entity is awoken as well until the awakened being is asleep again or out of the Empty.

Season 13 appearance
In The Big Empty, after the Seraph Castiel is awakened by Jack's telepathic call, the entity is awakened again. It arose in the form of a pool of dark liquid inside the Empty after Castiel walked by before taking on a vague humanoid form. The Entity followed Castiel as he made his way through the Empty, though he sensed the entity's presence and called out to it.

The entity took on Castiel's form to communicate with him directly, though it spoke with a distinct voice and accent. The entity identified itself as "just your friendly, neighborhood cosmic entity" and stated that it has taken on Castiel's form as its real form is too frightening. Indicating that its true form induces complete insanity, even to angels.

The entity explained to Castiel that the Empty is what existed before everything, including God and the Darkness and Castiel was "soaking in it." The entity told Castiel about how every angel or demon that has ever died was in an eternal sleep inside the Empty but was confused by how Castiel was awake.

According to the entity, "in all of forever", nothing has ever awakened inside the Empty as it mentioned its slumber being disturbed by his awakening. Castiel didn't know and suggested that the Winchesters must have made a deal, but the entity disbelieved this and stated that only it has power over the Empty with not even God having power there.

The entity then put its hand to Castiel's forehead and painfully went through his memories in an attempt to find out what could have woken up Castiel.

Afterwards, the entity explained to Castiel, who remained in pain, what he did and that it wanted Castiel back to sleep.

It described Castiel being awake as a trapped gnat that was loudly buzzing in its head as Castiel realized from the entity's description that him being awake was painful for the entity. This was confirmed by the entity, stating that if Castiel could not sleep, then the entity could not sleep as well.

The entity insisted that it likes and needs sleep, causing Castiel to suggest that it get rid of him by sending Castiel back to Earth. The entity instead suggested that it throw Castiel so deep into the Empty that he could not bother it anymore, but Castiel recognized that the entity was bluffing. Castiel challenged that the entity's plan would not work as the entity would have already done it. The entity acknowledged that Castiel was right, but refused to send him back, telling Castiel that "it's not part of the deal."

The entity stated that it has gone through all of Castiel's memories and knew everything there is about him and claimed that there was nothing back on Earth for Castiel.

The entity grasped Castiel's head and painfully showed Castiel visions of his grace being stolen by Metatron, his death at the hands of Lucifer, the Escape of the Leviathans and Castiel returning the souls to Purgatory. The entity struck down Castiel, attempting to convince Castiel to he was worthless so he would return to sleep.

However, Castiel refused the entity's demands and declared that no matter what the entity does, he will fight it for eternity if he was not released. The entity angrily denied Castiel's demands as Castiel continued to demand for his release from the realm.

Castiel later awakened in a meadow on Earth and realized that the entity has resurrected him and rebuild his vessel as Castiel had demanded.

In Tombstone, the resurrected Castiel tells the Winchesters that he annoyed an "ancient cosmic being" so much that it sent him back.

Personality
The Entity was shown to have a sarcastic manner as shown in its meeting with Castiel.

It showed frustration at its failures to break his spirit in an attempt to get him to give up on wanting to live again so it could return to its peaceful slumber.

When this didn't work, it attacked him out of frustration and called him worthless, which proved unsuccessful.

The entity was very angry at Castiel's defiant attitude but finally complied in annoyance, to resurrect Castiel to be able to return to its slumber. This shows that the entity is somewhat impatient.

Powers and Abilities
Being the supreme ruler of the Empty, the entity possesses immeasurable supernatural power, allowing it to do almost anything it wishes within its own realm.

Nigh-Omnipotence (within the Empty) The Entity has the power to do practically anything and has complete control over the Empty. The entity claims that not even God has strings on the Empty and all within it. However, the entity lacks the ability to force something that has awakened in the Empty back to sleep and must either convince them to return to sleep on their own or expel them.

Nigh-Omniscience
It knows about the world and what happened before its creation. Despite this, even it couldn't figure out why Castiel had awoke in what it considers all of forever.

Shapeshifting
Due to its true form being too terrifying or maddening for anything's eyes, the entity can take on the form of the being it is speaking to, though it speaks with a distinct voice instead of mimicking the being's voice.

Super Strength
The Entity was able to effortlessly overpower Castiel, though Castiel was weakened from his mind being painfully read.

Telepathy
In order to learn more about Castiel, the entity painfully dug through his memories. The entity later used this power to show him some of his failures in life in an effort to convince Castiel that he was worthless and should go back to sleep.

Resurrection
The entity was able to resurrect Castiel, returning him to Earth in the process.

Highly Advanced Reality Warping
The cosmic entity is able to create matter out of nothing as it fully rebuilt Castiel's vessel, which was previously burned and destroyed with no visible damage leftover.

Weaknesses
Although it is the ruler of the Empty, it has a few weaknesses as well.

Awakening of The Empty Inhabitants As long as the inhabitants of the Empty sleep, so does the entity itself. However, if even a single inhabitant is awake, it also wakes up the entity from its sleep. Furthermore, having waking inhabitants in the Empty causes it pain.

Sleep Deprivation
Being in deep slumber since before all existence, the entity can be severely disturbed if it cannot rest. Castiel claimed, while he cannot beat the entity, he can stay awake to lay pressure to it.

Quotes
"If you can't sleep, I can't sleep. Yeah? And I like sleep. I need sleep."

"I'm just your friendly neighborhood cosmic entity."

"Well, I show up in my real form, and you freak out, rip out your own eyes, et cetera. That would be embarrassing, wouldn't it, for both of us?"

"You see... before God and Amara. Creation, destruction, Heaven, Hell, your precious little Earth... what was there?"

"I have tiptoed through all your little tulips. Your memories. Your little feelings. Yes. I know what you hate. I know who you love. What you fear. There is nothing for you back there."

"So, think harder, wreck that perky little brain of yours!"

"Okay, I wreck it for you!"

"You know, since we're pals, there's something I gotta know. I just gotta ask."

"What I want is you to shut up!! I want... having you awake is like a gnat right up here and it's trapped. And it's buzzing."

"Or I throw you so deep in the empty, that you can't bother me anymore."

"Why are you awake? Cause fun fact, in all of forever, nothing ever wakes up here. I mean ever. And second fun fact, when you woke up, I woke up. And I don't like being awake. So, what's up, smart guy?"