Café de Nuit

How would you do Ravenloft in Star Trek? Is the entire thing one planet? Is the Core a solar system? Is each domain its own planet? Is it, rather, a fleet of starships, each darklord captain over a crew cursed by an anomalous subspace mist? What of individual characters?

If I was doing a Star Trek/Ravenloft crossover I’d start it as a holodeck adventure. Then slowly make the crew realise that they aren’t on the holodeck any more and grow the horror from there. Phasers are looked at as magic wands which isolated them from the locals. The universal translators malfunction and not only can they not communicate with the locals, they can’t communicate with each other (if they aren’t the same race). More bizarre races like Ferengi or Klingons are shunned, whilst Vulcans are mistaken for elves.

The crew are shown that the utopia of the Federation and their lives and values mean nothing in Ravenloft.

Off the top of my head, I like the idea of each domain being a planet, although more likely a planetoid and the clusters are various solar systems. Galactic dust block sensors and probes and the only way through it is with the help of the vistani, nomadic spacefarers. Each domain is like a captured point in time where the ages pass, but no advancements seem to be made.

I like the idea of B'Elanna Torres' personal vision of Greth'nor, Klingon Hell.
A powerful spaceship with mighty weapons and warp capacity... stuck in one place. Unmoving. Forever.

According to all systems, the ship is stuck in a stable geosynchronous orbit. In truth, it's trapped in a domain that resembles a pocket of space, with a few asteroids and stars in the distance.
On occasion, other domains might come within beaming or shuttle range, but none of them have the machinery needed to free the ship, and crews can get lost - or worse - down there.

So many ways really though I’d mostly focus on ship and starbase based ones. More of a TNG fan, but there’s a few episodes/stories there that could be adopted.

There was that alternate universe Enterprise from a universe where the Borg had overrun the Federation. Maybe they find you, or you arrive there. You can’t leave. The Captain is impressing any new people into service as crewmembers. This is just the least of what he’s willing to do to hold off the Borg. Maybe he’s trading them magic or fantasy as some sort of long shot, long game to victory.

There was another episode where these parasites had been taking over Starfleet, and they were going around trying to implant other officers with the parasite. Maybe everyone is aware, but there’s no way to determine who is what except by judging their actions.

If you want to let your Star Trek campaign be more Ravenloft, you could let the bold crew of the USS Ezra explore a mysterious, unknown nebula which turns out to have it's own set of natural laws (quite similar to the Xindi Expanse from Star Trek Enterprise), the main being that you can't leave it easily (you always end up within it's gaseous vapors). The 'domains' could be planets, asteroids and ships (actual ghost ships). You could take traditional Star trek monsters like the salt vampire (the last of it's kind), changelings or Borg to replace Ravenloft ones like vampires, doppelgangers and zombies. Or make Ravenloft villans like Ezan the Mad into one of the reality twisting beings (like Q) of Star Trek your Pc'S adversaries ("Welcome to Planet Vechor! I'm your host, Emperor Ezan the Glorious. What entertaining games should we play? What? Of course I'm not Vulcan..."). Many cultures have already stranded in the nebula. Planet Sithicus could be inhabited by a culture of lost Vulcans (who were already proposed as substitute for elves. I think Tellarites make good dwarves by the way ), while Planet Darkon is inhabited by the descendants of several federation vessels, so it's a multi-cultural world similar to a federation world, but as seen 'through a mirror darkly' .

The Voyager episode called "The Void" comes to my mind. A bunch of ships are trapped in a pocket of space from which they cannot escape, and they must steal from each other to survive. There are also native creatures that stow away on trapped ships. Add in a darklord that cannot control his own borders, and this could make a fair Star Trek Domain of Dread.

That sounds like a Star Trek version of Saragoss.