From publisher blurb:
They pull you into blackened depths, leap at you from shadows, dive at you from the skies, swarm from cracks in the walls, or break you to pieces as you scream for mercy. Then one night you realize the truth: you are the monster in the dream, and all the other monsters are your family.
In Beast: the Primordial, you take the role of one of the Begotten, descendants of an ancient nightmare creature called the Dark Mother. Beasts view each other -- and the other supernatural creatures of the World of Darkness -- as family, which means that Beast is explicitly designed to be crossover-friendly, both in terms of game mechanics and setting.
Beware, though. Just because the Begotten see the vampires, werewolves, mages, changelings, and mummies as kin, doesn't mean the feeling is mutual.