The Darkness include any magical beings with a primary drive to devour or collect.
Their parallel world is called Umbra. World name: Umbra. As they grow older, they grow more powerful, but their control (and sanity) tends to slip proportionately. Toward the ends of their lives, their physical forms can no longer take the strain of power coursing through them. Aged members of the Darkness tend to disintegrate into a sort of icy mist.
In Umbra, there is no light at all – it cannot exist there, physics be damned. Most members of the Darkness have the ability to eat just about anything, and that includes plague, radiation, dead bodies, etc. If well-trained, a member of the Darkness genuinely can devour to the cellular level.
Not all members of the Darkness eat that neatly, however. Here’s a scary example.
They prefer the cold; they also prefer the quiet. The People of the Darkness tend to live alone. What animals exist in Umbra tend to be completely silent.
They eat the powers of other Peoples; they tend to really, really, really like the taste of Fey, much to the latter’s dismay.
The Raven King is the oldest known member of the Darkness. He’s managed to live 15,000 years or so by devouring his own kind, so as you can imagine, he’s not very popular. This is one Shadow’s Breath you do not want to meet in person.