A Possible (Frightening) Connection
By Marco Dalmonte
First of all, think of Ravenloft as a demiplane existing inside the Dimensional Vortex, the Barrier that separates the Mystara Multiverse and the Old Ones living behind the first five dimensions. This concept is not so unlikely and in fact it is quite simple to understand:
True Nature of the Dark Powers Revealed (nearly )
So, that's my reasoning about the thing, but now you could ask: then
who are the Dark Powers, those who control the Mists (if they really control
them, that is)? Are they the Old Ones, the creators of the Multiverse and of the
Dimensional Barrier as we know from the Immortal boxed set? A frightening possibility,
certainly, but we know that the Old Ones are good and that doesn't seem the case of the
Dark Powers. Also, the Old Ones (according to the information gathered through various
D&D supplements) did create the Vortex and are able to bypass it whenever they want,
so they are not prisoners of the Mists, as the Dark Powers seem to be.
So, who are the Dark Powers?
My hypothesis is that they are somehow trapped inside the Vortex, unable to free themselves and capable to affect the other dimensions and planes only via the mists, transporting other people inside Ravenloft (not only evil people with a tragic background, but also innocents and heroes).
The Dark Powers and the Old Ones
Who placed them there? I suspect the Old Ones did. Probably the Dark Powers were once powerful entities (they still are, for that matter, all powerful within the Land of the Mists), perhaps even Old Ones, that threatened the very fabric of time and space with their actions or thoughts. So the Old Ones fabricated this dimensional prison of immense proportions to keep them there and to avoid much damage to their project, the Multiverse. Think of the Dark Powers as an entity much like the Lovecraftian beings of primeval origin (like Yog-sothoth, Nyarlathotep, Cthulhu and the like, only more cunning). This way you could make the equation: Dark Powers = Outer Beings (from Geoff Gander's Outer Beings scenario).
The Dark Powers' True Goal
What are the Dark Powers trying to do, then? The frightening idea behind their actions is this: they're trying to swallow the entire universe! Since they cannot escape their prison and since they're not even free to roam Ravenloft materially (there is a mysterious figure called Gentleman Caller who brings chaos and mischief throughout the land, but he's more like a sort of materialization of the Dark Powers, an avatar or an unholy child, not the DPs properly ), their only hope is to drag the whole Prime in the Vortex and to rule it inside there!!