My current personal version of this is based on the Magnus Archives. A quick summary follows:
The Dark Powers are unknowable entities who are the embodiment of fear. For reasons that cannot be comprehended by mortal minds, they capture creatures in their demi-plane and explore their fears. Some (willingly or unwillingly) become avatars of these fears. These are the dark lords. While the Dark Powers are eldritch beings, some scholars have given the monikers to discuss them. They are named based on primal fears all living creatures possess: The Darkness, The Stranger, The Slaughter, The Lonely, The End, etc. It it believed some can make contact with the Dark Powers, but often work through intermediaries called Vestiges. For reasons not adequately explained, most of the known Vestiges are encased in Amber Sarcophagi across the demiplane, with the largest concentration in the Amber Temple of Barovia. A few foolish scholars have made the error that Vestiges are the Dark Powers themselves. In truth, the connection between Dark Powers, Vestiges, and Darklords is a complex one full of contradictions, lies, and maddening half-truths.
It is a partial attempt to define the Dark Powers without making them knowable. It also attempts to thread the needle between different takes on the DP. They are something old, alien, and interested only in the exploration of our fears.
I like it!
I've been exploring my Shadowfell ideas lately and have turned to the Jungian concept of Shadow to recontextualive things. In the Jungian definition, to be very short with it, our Shadow are things we suppress about ourselves. This can be negative and positive, and includes things like impulses, thoughts, behaviors we don't act out, things we don't like about ourselves, things we have to suppress to do certain jobs, and so on.
The Dark Powers are things that sentient life has suppressed about itself since the dawn of senteince. The Shadowfell itself is a plane where all of this information collects and the Dark Powers have grown over time, being spliced and changed and warped by positive and negative effects across all time and space, and it turns out that, since life is Suffering, Dark Powers are a lot darker than otherwise.
Why the Dark Powers collect heinous people and lock them into Domains of Dread is not known, but there are theories from planeswalking scholars.
1.) The Dark Powers are doing what is in their nature; if they are born of suppression, they must suppress, and they suppress the most heinous things in creation (and whoever is misfortunate enough to be drawn into their Domains with them or afterward).
2.) The Dark Powers multiply by containing heinous people and steeping them in ever greater negativity. Eventually, the Dark Lord mentally adapts to their Domain and over comes it, becoming something capable of not just withstanding but manipulating the vast amount of negative information their Domain both absorbs and produces.
3.) The Dark Powers do this at the Raven Queen's behest, who mastered them when she fell into the Shadow and rose within it as her new godly self. The Dark Powers create Domains of Dread because within tragedies is contained the original memories of the Raven Queen; to understand herself, she must understand Shadow; to understand Shadow, she must understand Tragedy; thus she perpetuates the Domains of Dread (probably until the end of time).
These three theories are competing, but could also work in unison, and its really made the Shadowfell a more interesting place for me specifically to run games in. Its also let me greatly reimagine the aesthetics of the Shadowfell (and in truth, the Plane of Shadow is really more like the Plane of Heresy at this point; maybe I'll rename it and try and publish it some day...)
