Nephilim

"She's a Nephilim, an abomination."

- Metatron to Castiel

A Nephilim is a hybrid creature born 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.

Characteristics
As stated, Nephilim are the result of sexual reproduction between a human and an occupied angel vessel, the latter giving the offspring angelic properties. Nephilim are only created if their angelic parent has his or her grace during conception, which seems to be the source of what makes a Nephilim. If an angel mates with a human without its grace, the resulting offspring will be completely human. 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.

History
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, its 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 mistress 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 returned to his Cage, Kelly runs away, not wanting to abort her child despite the dangers.

Known Nephilims

 * Jane (deceased)
 * Lucifer and Kelly's unborn child

Powers and Abilities

 * Astral Perception - A Nephilim can perceive the true form of angels without harm.
 * 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.

Weaknesses

 * Primordial entities - Amara, God, Death and the Archangels could annihilate a Nephilim effortlessly.
 * Angel Blade - Castiel killed one with an angel blade.
 * Death's Scythe - It can kill anything.
 * The First Blade - When combined with the Mark of Cain, the First Blade can kill almost anything in existence, including Nephilim.