How does my homebrew campaign differ from Chaosium's setting?

Chaosium's Nephilim setting is heavily altered from the French version. It would be very hard to recap the French setting and compare the two, so I'm not going to do that. I'm just going to explain my homebrew.

I've decided to make a number of changes to Chaosium's setting for my homebrew setting. The major changes are:

The paredrus

The nature of the Nephilim has been changed from body-snatching parasites to higher selves created by the union of a human being and an elemental paredrus. All human souls, as well as all paredri, were originally part of the House of Guf. Awakening as a Nephilim reminds them of this: it is a revelatory and transcendent experience.

By itself, the paredrus is a mostly instinctive elemental beast driven by its passions. It is composed of a pentacle of the five elements, contrasting it against other elemental beasts that have only one or two. Likewise, the qualities of awareness, identity and will come from the human soul: Sol, or Solar-Ka.

The paredrus can attach itself to a sympathetic human being during moments of intense emotional weakness when the Solar-Ka is permeable. This host is someone who would benefit from the union, who desires the opportunity on at least an unconscious level, and has a life that already symbolically resonates with the paredrus' Dominant Ka. (E.g. a doctor beating themselves up over a patient they couldn't save would be an ideal candidate for incarnating a Faerim whose incarnations identified with Temperance.)

This union forms a microcosm of the Solar system with the paredrus' Ka-elements orbiting the human's Solar-Ka. The paredrus gains the human's awareness, identity, and will. In exchange, the human ego (a construct formed in early childhood) is dissolved and the higher self or super-ego can now emerge. This revealed higher self is the Nephilim. He or she is able to practice the Occult Sciences, channel past lives, and pursue the quests for Agartha.

Many secret societies believe the Nephilim are body-snatchers and have no problem murdering them or subjecting them to horrific rituals that mutilate their souls. 

This should help to make Nephilim more attractive to players. Nephilim are defined by their ties to the secret history and their extensive knowledge of the occult. This should make them an attractive option to experienced players.

Playable Selenim

I will include rules for playing Selenim. These are based on both Ian Young's archived public notes and the third edition of the French version. The Selenim practice three Occult Sciences of their own: Necromancy that allows the transgression of the boundary between life and death, Conjuration that allows the conjuring of black elementals from the nightmare lands, and Anamorphosis that allows the creation of an elemental familiar that can manifest its aspects upon the creator's own body a la metamorphosis.

I am adjusting the lore to be more inclusive of Selenim. Although the Selenim have traditionally been feared and misunderstood, the Great Awakening has resulted in the development of better relations between the Nephilim and their cousins. More open-minded Nephilim, such as the PCs, have accepted Selenim into their circles of friends. 

The Unnamed Arcanum has rechristened itself "Rebirth" in order to celebrate the rediscovery of Akhenaton's revelations. Although Rebirth only accepts those Immortals whose Dominant Ka is Black Moon, including both Selenim and Serpentaries (see below), it is possible for Selenim to join another Arcanum if they feel it suits them better. 

A number of former Death Initiates have decided to identify with The Tower because they feel it is a better fit for Nephren-Ka's original vision of protectors. Conversely, Rebirth has refocused its efforts on studying the Black Moon fields and the obscure sciences of the Black Moon.

As of the Great Awakening, it was revealed that not all Selenim are former Nephilim either! The natural Selenim are former mortals who merged with a black paredrus on the astral plane during a nightmare, turning them into Selenim.

Selenim may be an attractive option to players interested in a romantic/gothic protagonist.

The astrological Nephilim

The astrological Nephilim, or Ar-Kaïm, were first described in late second edition of the French before being included as player character options in the third edition. I have decided to incorporate them into my setting as well.

They are linked to the twelve Houses of the Zodiac (including the hidden thirteenth sign of Serpentarius), to the Astral plane, and to the Earth's Grail. They are able to cultivate all eight Ka in their magical aura, including Black Moon-Ka and Saturnian-Ka. They practice their own form of magic known as Talents instead of the Occult Sciences, though no law prevents them from learning the latter. Indeed, they have developed a new Occult Science unique to them known as Archemetry.

However, the Ar-Kaïm don't incarnate the same way that the Nephilim do. They can only reincarnate within their own descendants, which must be done by ritual while their current incarnation lives. They lack Stasis Objects and cannot channel past lives the way that Nephilim do. 

They are defined by their youth, inexperience, and lack of strong ties to the occult scene. This can make them an attractive option to beginner players.

Hope you enjoyed!