Nephilim

"The father has wings, the mother is a primate, and this child has a human soul mixed with angelic grace."

- Ishim lying to his flight of angels

A Nephilim is a hybrid creature conceived by an angel and a human. The offspring contains a mixture of human soul and angelic grace as a source of power, inherited from both of the parents. Whenever a Nephilim grew into their power, entire worlds died. As a result, conceiving a Nephilim is strictly forbidden by laws of Heaven and the punishment is death for the celestial parent along with the child.

Characteristics
As stated, Nephilim are the result of sexual reproduction between a human and an angel occupying a vessel. Nephilim have glowing eyes like an angel, although their glow is somewhat dim and grayish in color as opposed to the bright white or bluish-white glow of regular angels. A Nephilim's eye color is also related to the angel who sired them; whereas Lucifer's eyes were red, his Nephilim child's eyes were golden.

Nephilim were stated to be have been quite destructive with their powers as Castiel and Mirabel from over a hundred years ago stated that whenever Nephilim grew into their full power, entire worlds died causing them to be forbidden by the oldest laws of Heaven. As a result, they are considered as unholy beings and abominations. A mother pregnant with a Nephilim can ignite a bible upon physical contact. Dagon revealed to the mother of Lucifer's Nephilim child that carrying a Nephilim is always fatal to the human mother.

Theoretically, removing a Nephilim's grace will turn them into a normal human as removing the grace of an angel would turn them, effectively, human. It is unknown if the procedure is effective. Though Jack had his Grace extracted and absorbed by Lucifer, despite being powerless afterwards, Castiel revealed that his Grace would recharge in time, throwing whether or not they become human into question.

It's later revealed that the Nephilim's grace is what holds their human and angel halves in balance and, when they lose it, their two halves come in conflict with each other, causing the Nephilim's body to shut down progressively. The only way to revert that is for the Nephilim to recharge their grace.

While their grace is an angel's source of power, a Nephilim has their parents Grace mixed with a human soul causing them to be superior to angels In terms of power. When fighting Jane, the angels Metatron and Castiel were easily overpowered and thrown around by her, only winning when Castiel caught her by surprise from behind with an angel blade. The Nephilim lore states, as revealed by Sam Winchester that a Nephilim will eventually become more powerful than the angel that sired them.

Due to their human souls, a Nephilim, at least when their Grace has been removed, can go to a human afterlife such as Heaven or Hell though the Shadow believes that they belong in the Empty due to their half-angel heritage. As seen in the case of Jack, in Heaven they are able to sense the true nature of the realm around them and can leave their own personal Heavens and travel to other Heavens that they choose.

History
The last time that there were Nephilim walking the Earth, God himself had to intervene in order to remove them from the planet.

In Clip Show, Metatron leads Castiel to the Nephilim Jane and tells him that killing a Nephilim and cutting out its heart is the first of three trials to close the Gates of Heaven. After a fight, Castiel kills Jane with an angel blade through the throat. In Sacrifice, it's revealed that a Nephilim's heart is actually part of a spell to expel all angels from Heaven.

In LOTUS, while possessing Jefferson Rooney, the President of the United States, Lucifer had sex with his lover Kelly Kline and conceives a Nephilim. The conception is felt by all angels as a surge of celestial energy, causing the angels to panic on "angel radio." After Lucifer is taken prisoner by Crowley, Kelly runs away from the Winchesters in order to protect her child. Dagon, one of the four Princes of Hell, begins safeguarding Kelly a few months later. In The Future, the child resurrects his mother after she commits suicide and she becomes convinced that the child is good, not evil as everyone believes. The child chooses Castiel as his new guardian and aids the Seraphim in killing Dagon. Afterwards, Castiel becomes convinced the child needs to be born with his powers intact and tells Kelly that the child showed him "the future".

In Lily Sunder Has Some Regrets, a group of angels arrived on Earth in order to put an end to a Nephilim's existence. However the child was not a Nephilim and they were tricked by their leader. It was revealed that by the oldest laws of Heaven, producing a Nephilim was forbidden and its penalty was death. During this period, Castiel claimed that entire worlds died when Nephilim came into their power, branding them "world destroyers."

In The Scorpion and The Frog, while trying to find Jack, Sam and Dean discovered that the Queen of Sheba was also a nephilim and that King Solomon created a spell to track Nephilims, allowing him to always know where his lover was.

Known Nephilim

 * Jack Kline
 * Jane
 * Queen of Sheba

Powers and Abilities
"Castiel: Nephilim grow up. They grow into their power, and then... Mirabel: Entire worlds die."

- Castiel and Mirabel The power level of a Nephilim depends on how strong their angelic parent is. Generally speaking, Nephilim are more powerful than angels themselves. Nephilim lore states that by full power, they will be stronger than at least their angelic parent. It has been stated that Nephilim are immensely powerful beings and, when they grow up, will have grown into their full power which makes them capable of being very dangerous. The angels' themselves years ago stated that whenever a nephilim grew into their power entire worlds died. While Castiel stated even an ordinary nephilim is "one of the most dangerous beings in all creation", he stated that a Nephilim parented by an archangel would possess unimaginable levels of power beyond any comprehension. This was proven by Jack, Lucifer's son, when he was able to use several powerful abilities even before he left his mother's womb. He is capable of opening rifts to Alternate realities and according to Duma, is strong enough to create new angels. Jack was also able to destroy the most powerful Archangel in creation, while in a weakened state. According to Miriam, Jack can do "almost anything" but indicates that there are some limits to his powers. They are so powerful that at one point, when nephilim were walking the earth, God himself had to intervene in order to remove them.
 * Astral Perception - A Nephilim can perceive the true form of angels, such as perceiving their halos.
 * Super Strength - Their angelic ancestry endows Nephilim with enhanced strength sufficient to overpower and even toss common angels around. One was able to throw around Castiel, a wounded Seraph at the time. Jack was able to rip off the handle of a triple-locked door with ease.
 * Healing - Jack was able to heal his mother's slit wrists and massive blood loss from the womb. He also healed Castiel's injuries in a matter of seconds while empowering him.
 * Resurrection - Jack was able to resurrect his mother at the same time he healed her. However, Miriam indicated that Jack could not resurrect an angel that was "all the way dead" despite his vast power.
 * Power Granting - Jack was able to temporarily empower Castiel, a Seraphim, while Castiel held his mother's hand so that they could take down Dagon together.
 * Super Strength - While empowering Castiel, Jack granted him the strength to effortlessly overpower the Prince of Hell Dagon.
 * Power Negation - While empowering Castiel, Jack granted him the power to render Dagon completely powerless.
 * Pyrokinesis - While empowering Castiel, Jack granted him the power to burn Dagon to ashes, a feat previously unseen with any other character.
 * Portal Creation - Jack's birth caused a rift to open into an alternate reality. Working with a dreamwalker, Jack was capable of opening rifts to alternate realities at will. However, due to Kaia Nieves flashing between one reality and another, Jack, Kaia and the Winchesters ended up in three separate locations, two of which were the alternate realities Kaia was flashing between.
 * Reality Warping - Under the influence of a disguised Asmodeus, Jack was able to open a Hell Gate in an attempt to release the Shedim. However this required Jack's full concentration and when his concentration broke the Hell Gate closed.
 * Rapid Aging - Jack was able to grow into a young adult soon after birth.
 * Telekinesis - Jack was able to generate immense waves of telekinetic force when threatened. After using this ability against Buddy, Jack gained control of this power and was able to use it at will. After practicing with it, Jack was able to create a small telekinetic shockwave to knock the Winchesters and Castiel to the ground and later blasted an angel with such force that she flew through a glass window and a brick wall. With another angel, Jack was able to telekinetically force the angel to stab himself with his own angel blade to kill the angel.
 * Immunity - Despite having an angelic heritage, Jack displayed an immunity to the angel banishing sigil, a weakness that affected even his father. He was also immune to angel warding.
 * Invulnerability - Jack displayed the ability to take an angel blade to the heart and survive unharmed. Jane did not possess this level of invulnerability as an angel blade through the throat was able to kill her. Jack was also able to stab himself with a butcher knife several times with no real harm.
 * Regeneration - After removing the angel blade from his heart, Jack was able to heal the wound in seconds. The wounds he inflicted upon himself with a butcher knife healed in seconds also.
 * Super Senses - Jack displayed the ability to clearly hear a conversation that was taking place on the opposite side of the room.
 * Teleportation - When Jack grew upset, he was able to teleport away. In Tombstone, the sound of wings can be heard when Jack intentionally uses the power, implying he has wings.
 * Terrakinesis - In response to Jack's anger at Asmodeus, the ground began to shake.
 * Telepathy - Jack was able to telepathically call out to Castiel in The Empty, awakening him from his slumber. By touching a person's head, Jack was able to connect with their minds, causing their eyes to glow as well as the veins on their faces. Doing this, Jack was capable of sharing images with the person and seeing what a dreamwalker was experiencing through their powers.
 * Mind Control - Jack was able to force Lucifer to tell him the truth against his own will.
 * Precognition - Jack had a premonition of Castiel's later confrontation with Dagon which he was able to share with his mother.
 * Sedation - Like an angel, Jack could put people to sleep with just a touch.
 * Supernatural Concealment -  When Jack does not want to be found, his powers are subconsciously concealing him from other beings. This was shown by the fact that Asmodeus was incapable of tracking his whereabouts.
 * Molecular Combustion - While Jack was combining powers with Kaia, the two emitted a yellow glow while opening a rift that caused six nearby angels to disintegrate to dust. On his own, Jack was able to cause Zachariah to combust just by clenching his fist while holding Zachariah with telekinesis and combusted three more angels in mid-air by emitting energy waves similar to his telekinesis into the sky.
 * Thermokinesis - Jack was able to cause metal bars to melt with a touch.
 * Illusion - Jack was able to alter the images of his shadow puppets to entertain young children.

Weaknesses

 * Heavenly Portal (possibly) - Due to Jack possessing a human soul, the angels believed that taking him through the portal while Kelly was pregnant with him would effectively destroy Jack. Later on after Jack teleported away from the bunker to protect the Winchester and Castiel from himself, Castiel asked Duma if Jack was in Metatron's old cell in Heaven as he believed that the angels have taken him.
 * Angel Blades - Castiel killed one with an angel blade. However, Jack Kline could not be killed or even harmed by an angel blade.
 * God - Last time Nephilim were walking the Earth, God had to intervene in order to remove them.
 * Grace Extraction  -  Removing a Nephilim's angelic grace could possibly turn them effectively fully human and render the Nephilim virtually powerless. Lucifer was able to extract some of Jack's grace and leave him powerless. Extracting a Nephilim's grace also renders their bodies unstable, as their human half and angel half will start to attack their cells, which will cause them to die unless their grace is restored.
 * Angel Radio - Hearing "angel radio" caused Jack debilitating pain.
 * Unexpected Mechanical Trauma - While Jack has the superhuman endurance to shrug off bullets and knife wounds, Jack can be knocked unconscious or temporarily stunned with pain by physical forces when he is caught off guard. Sam had once knocked Jack unconscious by electrocuting him with a Taser. A shapeshifter was able to knock Jack unconscious by hitting him in the head with a fireplace poker.
 * Very Heavy-Angel Warding - Jack's powers were severely weakened by the powerful warding in Michael's fortress, leaving him vulnerable to the powers of Michael and Zachariah. The warding was so much that when Jack attempted to use even some of his more easily controlled powers, he could do nothing. In a spot where the warding was weak, Jack was capable of using a weaker ability to melt metal bars.
 * Archangel Blades - Lucifer was able to use the blade on Jack when extracting his power from him. The blade most likely worked on Jack due to his archangel heritage. As a result, Jack's powers were depleted and would recharge at a slow rate.

Appearances

 * Season 8
 * Clip Show
 * Season 9
 * Heaven Can't Wait
 * Season 12
 * LOTUS
 * Lily Sunder Has Some Regrets
 * Stuck in the Middle (With You)
 * Family Feud
 * Somewhere Between Heaven and Hell
 * The British Invasion
 * The Future
 * Twigs & Twine & Tasha Banes
 * All Along the Watchtower
 * Season 13
 * Lost & Found
 * The Rising Son
 * Patience
 * The Big Empty
 * Advanced Thanatology
 * Tombstone
 * War of the Worlds
 * The Scorpion and The Frog
 * The Bad Place
 * Wayward Sisters
 * Breakdown
 * Various & Sundry Villains
 * Devil's Bargain
 * Good Intentions
 * The Thing
 * Bring 'em Back Alive
 * Unfinished Business
 * Beat the Devil
 * Exodus
 * Let the Good Times Roll
 * Season 14
 * Stranger in a Strange Land
 * Gods and Monsters
 * The Scar
 * Mint Condition
 * Nightmare Logic
 * Optimism
 * Unhuman Nature
 * Byzantium
 * The Spear
 * Nihilism
 * Damaged Goods
 * Prophet and Loss
 * Lebanon
 * Ouroboros
 * Peace of Mind
 * Don't Go in the Woods

Trivia

 * The first part of a spell to expel all angels from Heaven is to "cut out the heart" of a Nephilim. According to Crowley's translation of the spell from the Angel Tablet, the Nephilim's heart itself is one of the three ingredients.
 * The only Nephilim on Earth, Jane, in Season 8, was at least 20 years old. As angels didn't typically intertwine on Earth during the time of her conception, the only angels present on earth were Cherubs, Gabriel, Metatron, and what remained of the Grigori. As the Grigori were responsible for producing the Nephilim in lore, it is likely that she was fathered by one of these angels.
 * An alternative is that like Lucifer's son, Jack, most or all Nephilim have the ability to rapidly age to adulthood. It is unknown if this ability is unique to Jack, as he is fathered by an Archangel.
 * The word "Nephilim" (נפילים) is actually plural in Modern Israeli Hebrew. The singular word is "Naphil" (נָפִיל), which means "giant" or maybe "monster". In Biblical Hebrew "Nephilim" (נפילים) might be an abstract singular noun that has plural form and that expresses the concept of naphil-ness. If naphil means monster, then nephilim means monstrosity as a Biblical Hebrew singular-sense abstract plural. Likewise, the apparent plural Elohim (אֱלֹהִים) is used as a name of God in Hebrew, but really it is an abstract noun, to wit, divinity, from a singular word for a god, to wit, eloah (אֱלוֹהַ).
 * It was revealed in The Future that a Nephilim only needs 5 months before they're born.
 * It is unknown where Nephilim go after death.
 * From The Shadow's attempts to claim Jack, it seems Nephilim go to The Empty but its unknown if that went for all Nephilim or if it was part of its grudge against Castiel.