The Dark Powers are the strange, god-like entities that rule over the Demiplane of Dread in Dungeons & Dragons. In the meta of the Ravenloft setting, they are literally the architects of everything, assembling their ever-expanding patchwork world and building it around Darklords, tweaking reality on a domain-by-domain basis to ensure proper "thematic purity", nerfing magic, fueling curses, and literally being the reason why this setting functions differently to any other D&D setting.
Traditionally, the precise nature of the Dark Powers is left ambiguous; what they are and what they want, or even if they're real at all, is the DM's prerogative. It adds to the malleability of the place, much like the concept of "Dread Possibilities" added in various splatbooks. Furthermore, figuring out what they want is complicated by the moral ambiguity of the things they do. Some argue they wish to punish the evil, as seen with the way that Darklords are rendered incapable of leaving their domains. Some argue that they seek to build an army from the most evil beings in the multiverse... but that doesn't make sense because lots of monsters in the wider multiverse are never touched by the Mists of Ravenloft. Some argue that they want to torment the innocent, but then, why does being evil always end up sucking so much? They really are a "build your own" kind of kit.
That said, a few sources have broken tradition on this account.
The first was a Ravenloft tie-in novel called "Lord of Necropolis", focused on Azalin. In this novel, it's claimed that the Dark Powers are actually divided into two camps of different entities; one good and one evil. The benevolent entities, referred to as "The Others", seek to protect the innocent and punish the wicked, whilst the malevolent Dark Powers have the other intention, and seek to entice people to act with evil. The novel was panned, as much for defining who the Dark Powers were as for its ridiculous claims that the entire Demiplane of Dread was actually created solely to torment Azalin, which makes no sense given he's not the first Darklord or the most important.
Previews for Masque of the Red Death said the Red Death was a Dark Power exiled by the others for some unknown crime. This information is not remotely present in the final product, though never contradicted and William Connors said in an interview with Monte Cook the Red Death being a Dark Power remained canonical. While the exact nature of the Red Death isn't clear (in the sense it has no explicitly defined abilities or limits), it has a lot more said about it than the Dark Powers proper, so the sub-setting might provide useful information if you treat this bit of info as canonical. Of particular note is that sealing away the Red Death is actually considered plausible by those in the know, and successfully happened at the end of RPGA's Living Death series via an Epic Spell involving several artifacts. This indicates that if the Red Death is indeed a Dark Power, then sealing the others may be plausible as well. That said, the Red Death differs from standard Dark Powers in one critical detail: Where the Red Death actively seeks to corrupt the people of its prison (Any use of magic, even something as selfless as using Cure Light Wounds to save someone from an accident, provokes a dark powers check on Gothic Earth) the Dark Powers of Ravenloft proper explicitly "never actively seduce the righteous into evil" (this may very well be the crime that got it banished in the first place).
The Dungeons & Dragons 5th Edition adventure, Curse of Strahd, an updated re-release of the original I6: Ravenloft, appears to present the Dark Powers as being vestige-like remnants of various evil entities, physically sealed inside amber sarcophagi which lie in a temple dedicated to their lingering evil, but this may be merely conflation because of poor clarification. 5e had retconned that Strahd made the deal to become a vampire with the vestiges which were situated in the prime material plane instead of beseeching the Dark Powers, and then the Powers stole the land of Barovia which happened to be where the vestiges were situated. So now we know slightly less about the nature of the Dark Powers.
Van Richten's Guide to Ravenloft reveals more information about the Dark Powers than any previous book but also says that it is up to the DM to decide what the true nature of the Dark Powers and provides three different suggestions about what their true nature is so don't take what it reveals as absolute fact. The Dark Powers may be amoral guardians protecting the multiverse from the Darklords but not caring about the suffering they cause within their prisons. Or they may be evil architects tormenting the Darklords for their amusement or to feed on them or test them for worthiness for promotion to Dark Power. Or they may be undying remnants of evil gods locked in amber sarcophagi like those in the Amber Temple scattered throughout the domain of dread that are trying to revive themselves. The book seems to mainly treat the last option as the "correct" one. It reveals that some of the names of the Dark Powers include Osybus, Shami-Amourae (an obscure Demon Prince), and Tenebrous and that Osybus is a former mortal priest of the Dark Powers who became a Dark Power himself after his disciples betrayed and killed him. His disciples were cursed to lose the immortality he had given them when they least expected it. The Dark Powers told them they they would be free from the curse if they helped the Dark Powers take over the world by creating a vessel for them to inhabit. They chose Strahd to be the vessel and caused his fall into evil and his discovery of the Amber Temple where he became a vampire, but the Dark Powers imprisoned Strahd in the mists instead. The priests of Osybus are still trying to find a way to release Strahd from the mists to conquer the world in the name of the Dark Powers to get their immortality back.
|The Deities & Religions of Ravenloft|
|Good||Brigantia - Ezra (Pure Hearts)
The Overseer - Ra
|Andral - Belenus
Diancecht - Osiris
|Neutral||Divinity of Mankind
Manannan mac Lir
Ezra (Home Faith) - Yutow
Ezra (Erudites) - Hala
The Ancestral Choir
|Lugh - Mytteri|
|Evil||Anubis - Ezra (Zealots)
Math Mathonwy - The Lawgiver
Set - Zhakata
The Eternal Order
|Cat Lord - Erlin |
Kali - Morrigan
The Spider Queen
The Wolf God