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 inherited from both of the parents. 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 are considered as unholy beings and abominations. A mother pregnant with a Nephilim can ignite a bible upon physical contact. Also, according to Dagon 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.

According to Nephilim lore, the Nephilim will eventually become more powerful than the angel that sired them.

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
 * Jane (deceased)
 * Queen of Sheba (deceased; mentioned only)

Powers and Abilities
The power level of a Nephilim depends on how strong their angelic parent is. Generally speaking, Nephilim are more powerful than angels themselves. It has been stated that Nephilim, when they grow up, can grow into their powers which is very dangerous, with Castiel classifying them as "one of the most dangerous beings in all creation". However, he stated that a Nephilim parented by an archangel would possess unimaginable power beyond 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. According to Miriam, Jack can do "almost anything" but indicates that there are some limits to his powers. Nephilim lore states that when the Nephilim are at full power, they will be stronger than their angelic parent.
 * 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 grant the same Seraph the strength to easily overpower a Prince of Hell.
 * 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.
 * Precognition - Jack had a premonition of Castiel's later confrontation with Dagon which he was able to share with his mother.
 * 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, the child granted him the strength to effortlessly overpower the Prince of Hell Dagon.
 * Power Negation - While empowering Castiel, the child granted him the power to render Dagon completely powerless.
 * Advanced Pyrokinesis - While empowering Castiel, the child granted him the power to burn Dagon to ashes, a feat previously unseen with any other character.
 * Reality Warping - Jack's birth caused a rift to open into an alternate reality.
 * 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.
 * Immunity - Despite having an angelic heritage, Jack displayed an immunity to the angel banishing sigil, a weakness that affected even his father.
 * 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.

Weaknesses

 * Angel Blade - Castiel killed one with an angel blade. However, Jack 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 (possibly) -  Removing a Nephilim's angelic grace could possibly turn them effectively fully human and render the Nephilim virtually powerless.
 * Electrocution - Sam was able to render Jack unconscious with a taser blast.
 * Angel Radio - Hearing "angel radio" caused Jack debilitating pain.
 * Nephilim Tracking Spell - This spell was able to locate the Queen of Sheba.

Appearances

 * Season 8
 * Clip Show (Jane; first and last appearance)
 * Season 12
 * LOTUS (Jack; mentioned only)
 * Lily Sunder Has Some Regrets (Jack; mentioned only)
 * The British Invasion (Jack; mentioned only)
 * The Future (Jack; presence only)
 * Twigs & Twine & Tasha Banes (Jack; mentioned only)
 * All Along the Watchtower (Jack; first physical appearance)
 * Season 13
 * Lost & Found (Jack)
 * The Rising Son (Jack)
 * Patience (Jack)
 * The Big Empty (Jack)
 * Advanced Thanatology (Jack; mentioned only)
 * Tombstone (Jack)
 * War of the Worlds (Jack; mentioned only)
 * The Scorpion and The Frog (Jack and Queen of Sheba mentioned only)
 * The Bad Place (Jack)
 * Breakdown (Jack)
 * Devil's Bargain (Jack)
 * Only the Best Intentions (Jack)

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 Reapers, 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.
 * The first two known Nephilims have a 4 letter name that starts with J.