Café de Nuit

I've decided for a forthcoming Ravenloft campaign that I will be DM'ing to start the campaign on a homegrown prime world, then have the world itself get sucked into the mists during the course of the campaign, so the players actually get to experience the before and after. The main city of this realm is a port city ran by a syndicate of merchant houses who ostensibly work together, but constantly seek to usurp each other behind the scenes in a machiavellian game of houses. Although I have enough detail, sideplots, and minor villains to keep the party playing in the sandbox indefinitely (and getting sucked into Ravenloft will open innumerable other possibilities) I'm absolutely stuck on a good idea for a darklord and the tragic events that lead to the mists claiming this land. I want to work in the merchant war/game of houses aspect yet have a villain who is also supernatural and terrifying. I've been toying with the idea of a shadow dragon that lives under the city itself who is the real puppetmaster manipulating the House rivalries for his own gain, but I'm reticent to put a dragon in Ravenloft for stylistic reasons. Any tips, suggestions, or ideas to get my creative juices flowing again would be very appreciated.

What about using the Dragon, but he's stuck in Human form, and something like no matter how much treasure he accrues through the course of a day, it's always gone the next morning? There would clearly be more, and of a darker nature, to the curse but this might be the basis for making it work. I'm still mulling over a few other ideas as well.

Torn between the aforementioned dragon idea and a merchant lord who is in fact a serial killer.

I'd say the merchantman is a better option, although his terror tracks could lead him in the direction of becoming a creature of avarice like a dragon. Maybe a gothic Scrooge McDuck (oh yeah, I can find gothicism in Disney!) who has the curse you listed above for the dragon. A disappearing fortune could have ramifications to a regular businessman--they might just give up. But with an obsessive personality, I can see him throwing himself into bigger and bigger ventures, even criminal ventures, in an effort to circumvent a curse his ego will not let him understand.

Once pulled into the demiplane, a rivalry with the Boritsi trading company would be increasingly maddening, possibly driving him to rash decisions. As far as "becoming" a dragon, he need not quintuple in size and grow wings. He may develop the immunities of a dragon, while having somethign like his appetite change (roast 4 sheep and bring them to my private dining room). If he ever does get frustrated with business and think about giving up, scales begin to form on his skin and he face becomes distorted, scaring him back into the cycle of greed.

If by "sheep" you mean "people," then I like the idea.

I'm also considering taking the informaton I have on a city of feuding merchant houses and using it to flesh out/modify an existing domain. Port-a-Lucine in Dementlieu lends itself rather naturally to such a setting, and Dominic d'Honaire is precisely the type of villain I'm looking for, a manipulative mastermind lurking in the shadows. I'm probably going to tweak his history and abilities a bit to suit the campaign, but other than that he's fairly close to what I was looking for.
The idea for the merchant Houses is 9 merchant houses, one of each alignment and each with a different market niche. While they ostensibly work together for the good of the city, they constantly undermine each other behind the scenes and this occasionally even ecalates to outright war between the Houses. house of similiar alignment ally with each other, and oppose those of differing ethos. Dominic, of course would be the true puppetmaster, manipulating all of this machiavellian strife behind the scenes to further his own objectives. What do you think?