|“||The father has wings, the mother is a primate, and this child has a human soul mixed with angelic grace.||”|
— Ishim to his flight of angels
A Nephilim is a hybrid creature that is made up of a human soul containing traces of angelic grace. Every known Nephilim was created from the union of an angel and a human. Castiel stated that creating a Nephilim is forbidden; however, Metatron revealed in "Clip Show" that there was one existing on Earth. Metatron viewed this Nephilim as an abomination due to her existence being outlawed.
As stated, Nephilim are typically the result of sexual reproduction between a human and an occupied angel vessel. The offspring inherits its soul from its human parent and receives grace from its angelic parent. This grace gives the Nephilim access to enochian magic which, fueled by the power of its human soul, is far superior to the power of angels. 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 and its mother can also share certain special characteristics with that of its angelic father, such as burning bibles on physical contact. As was the case with Lucifer and Kelly the mother carrying his unborn child. It is also revealed by Dagon that carrying a Nephilim is always fatal to the human mother.
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 President of the United States Jefferson Rooney, Lucifer has 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 begins safeguarding Kelly a few months later.
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.
Powers and AbilitiesEdit
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 by a Nephilim parented by an archangel would possess unimaginable power.
- Astral Perception - A Nephilim can perceive the true form of angels.
- 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 a wounded seraph.
- Angel Blade - Castiel killed one with an angel blade.
- God - Last time Nephilim were walking the Earth, God had to intervene in order to remove them.
- Season 8
- Clip Show (first appearance)
- Season 12
- 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, 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 remains 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.
- It's indicated that the power of a Nephilim depends on how powerful their celestial parent was in "LOTUS".
- The word "Nephilim" is actually plural in Hebrew. The singular word is "Nephil".