Welcome back to the Ravenloft Corner!
Veteran gamers are familiar with the horrible dread that accompanies every sudden fog, knowing it could whisk them away from their comfortable campaign setting and into the nightmare that is Ravenloft. This is far from an isolated event, of course: most of the iconic NPCs of the setting are drawn from one or more existing campaign worlds, including Darklords such as Soth, Harkon Lukas, and Hazlik. Faerun, Greyhawk, al-Qadim, Dragonlance, Birthright: all these realms and more have been harvested for human occupants to bring to the Demiplane of Dread.
However, the Mists are not limited to D&D settings--they can reach anywhere. This makes Ravenloft the ideal realm for crossover stories. The sinister possibilities are endless. Jedi, gunslingers, or mad scientists: the sky's the limit if you really want to bring elements from one game setting into your Ravenloft campaign.
Alternately, instead of bringing another game into Ravenloft, you can introduce Ravenloft to another setting. Back in the day, being snatched away to the Demiplane of Dread for a single adventure was a common enough occurrence that it even had a name: Weekend in Hell adventures. For many other tabletop RPGs, this type of adventure can be just the thing to break up a stale routine.
To get you started, here are a few of my favorite possibilities for locations that you could bring an NPC or two from without breaking the setting egregiously.
1 -Star Wars
While lightsabers and blasters would be horrendously out of place, a single force-user would not be. Imagine the horror for a Jedi who escaped Order 66 only to find himself consumed by a bizarre stellar phenomenon which spat him out in Ravenloft. Now alone, in a world without the technology to which he is accustomed, he must battle against strange and arcane threats, with the inescapable feeling that this entire realm throbs with the pulse of the Dark Side. He can always sense malignant beings pulling the strings behind seemingly mundane misfortunes, but can never quite pin down their presence. Of course, the Dark Side would be much easier to tap into in Ravenloft, presenting him with an eternal temptation of vast power in exchange for his allegiance.
2- Doctor Who
Although all the Time Lords in our universe are gone (save for a couple), there were many at one point. As a race with a penchant for getting themselves stuck in pocket dimensions or alternate universes, it's not inconceivable one of them could have made it to Ravenloft. (It seems quite likely that at least one of House's victims might have had the wherewithal to fashion some means to escape House's pocket dimension, albeit to the even-less-inviting environment of the Mists.) Stuck with only the technology of the era, such a being might embody the nobler instincts of their kind, traveling the domains and righting wrongs. Of course, they might also fall prey to the obsession and hubris that frequently grips their race, drifting towards Mordent and the possibility of finding a way home amid the 'new science' of Dr. Mordenheim.
3- World of Darkness
Even without the Mists capturing someone against their will, the World of Darkness has plenty of ways for an unwitting character to find their way to Ravenloft. The Deep Umbra, the Far Realms, and arcane accidents of any variety could land a character in the setting. Characters from Vampire: The Dark Ages or Werewolf: The Wild West wouldn't even find themselves horribly out of place. Many tradition mages or changelings would be right at home as well. A pack of werewolves would have the fight of their lives in Verbrek, where virtually every inhabitant is fighting on the same level as they are. On the other hand, how much more dangerous would Strahd be while served by a small clan of Revenants, their own innate disciplines augmented by his potent blood?
Another setting with many gateways to alternate settings (crossovers with Call of Cthulu and Werewolf aren't just possible, they're canon adventures), posses from the Weird West could easily find their way to Ravenloft. Perhaps they even discover some dark connection between the Dark Powers and the Reckoners? Although their technology might be a bit out of place in, say, Darkon, the firearms of the period aren't so odd as to be fantastical to those of the western core. To fit with the diabolical nature of the realm, of course, 'black' magic such as hexes, mad science, and the undead abilities of the Harrowed should be more potent than normal, with the concurrent penalty of attention from the Dark Powers. Maybe it's even more likely to come back as Harrowed, if not so easy to maintain Dominion...
5- Harry Potter
Let's face it, magical accidents are obscenely common in the world of Harry Potter. Fortunately, magical denizens of that realm will find Ravenloft to be no huge adjustment. The need to hide themselves from non-magical beings will already be second nature, but the existence of the supernatural will be as well. In many ways, these witches or wizards might have an easier time blending in than outlanders from standard D&D settings do!
6- Warhammer 40k
While this one might seem unusual for such a high-sci-fi setting, it's actually fairly easy. Remember that the many worlds in the Imperium have a huge technological spectrum, broader even than that in Ravenloft. Characters from low-tech worlds (Inquisitorial retinues or Imperial Guard conscripts) make the easiest possibilities, since they are already ready to accept magic as fact, and are perfectly willing to accept having been pulled through a warp storm into a demon world with belief (although maybe not much happiness). The immensely powerful psychics of the Eldar race might send a single advance scout through a forgotten Webway gate, hoping to find a new location to colonize. Of course, such a scout could never report back and would be stranded in this strange new world. Perhaps most frightening is the notion of a transpossession victim manifesting not the aura of a succubus or the spikes of an osyluth, but the weeping sores of a plaguebearer or the mind-numbing allure of a keeper of secrets.
The world of the Mayhem game system bears much in common with Ravenloft and other D&D settings: there is a general medieval feel, the presence of magical beings, and a general lack of advanced technology. The Crimson Realms, as they are known, are far more open about their strangeness than other settings and Outlanders from that world would face several challenges. The bestial races would have to conceal their true nature, or be mistaken for escapees from the clutches of Frantisek Markov. The demonic and celestial races would be pursued diligently by hunters familiar with transpossession, or by Darklords, respectively. Even the fae or elemental races would find persecution in places like Darkon or Tepest.
That's far from an exhaustive list, of course. Crossover potential is ripe in some of the best known franchises of nerd culture, such as Game of Thrones, Wheel of Time, the Dark Tower series, or Middle Earth, as well as some more obscure ones that your PCs might not be familiar with, such as John Peel's Diadem series or the worlds of Robin Hobb. Whether you draw PCs or NPCs from such realms, crossovers remain an integral part of the Ravenloft formula, and the Weekend in Hell will remain a constant threat to PCs in any and every other game.
Hopefully, Frankie Drakeson will be back from his sabbatical next month, but until then, safe travels.
Jim Stearns is a deranged hermit from the swamps of Southern Illinois. In addition to writing for the Black Library, he puts pen to paper for High Level Games and Keep on the Heathlands. His mad scribblings can frequently be found in Quoth the Raven, as well as anthologies like Fitting In or Selfies from the End of the World, by Mad Scientist Journal. Follow him on Twitter @jcstearnswriter.
I am become death, destroyer of worlds.