The Darkness include any magical beings with a primary drive to devour or collect.
Their parallel world is called The home of the Darkness. More. In Umbra, there is no light at all – it cannot exist there, physics be damned. What animals exist in Umbra tend to be completely silent.
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.
And they do. They are a varied group, surviving on all kinds of things they devour: everything from blood to souls to sex to money to weapons will do, depending on the specific species. They eat the powers of other Peoples; they tend to really, really, really like the taste of Fey, much to the latter’s dismay.
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.