40K Background Changes

The Primarchs

 The Primarchs as they were created by the Emperor were not giants, rather they were powerful Warp souls, much like human souls but imbued with great psychic power and potential before the Chaos gods scattered them across the universe. The souls of the Primarchs resisted being torn apart in the fury of the Warp and eventually broke free into the materium. Being made by the emperor to have souls much like those of humans, the Primarch souls we born from human bodies through out the Imperium, with the genetics of their material parents but Warp souls stronger than any mortal save for the Emperor himself.

The Primarchs settled on diverse worlds and had featured which reflected their heredity, some were male and some female. They tended to be somewhat taller than their kin, but not exceptionally so except in certain cases where the influence of the Warp caused the Primach’s bodies to take an unusual shape. It was the power of their Warp souls that imbued them with might, not their physical forms. Their psychic might caused each to grow up healthy and strong, their psychic potential manifesting as superhuman physical prowess and intellect, though most developed powerful psychic abilities as well.

The Astartes
The

Khorne
There are psykers of Khorne, they are filled with seething rage and hatred which empowers their psychic abilities. These powers almost always manifest physically, such as enemies bursting into flame or telekinetic force smashing buildings and vehicles. Their psychic rage also flows through their veins with their blood, making them exceptionally strong and resilient.

Daemons
There are a wide variety of daemons of Chaos, most lesser daemons are not Blood Letters, Plague Bearers, Daemonettes, or Horrors of Tzeentch and most greater daemons are not Blood Thirsters, Keepers of Secrets, Great Unclean Ones, or Lords of Change. Most daemons have names and individual power sets, appearances, and abilities.

Dark Eldar
Dark Eldar have psychic abilities just like all other Eldar, with their strength fueled through sadism. They also have dedicated psykers who have tremendous power but need many souls to fuel their more powerful abilities.