1. An asteroid cluster with an evil murderoid (or astereater) ...

    The murderoid (which is sort of a living asteroid) goes around attacking spelljamming ships and deep within the asteroid cluster is its home where hundreds of wrecked ships lie in a horrible mess like a tiny sargasso of death...

    Trapped in the sargasso are a few survivors fighting to survive from the hordes of undead... There are also pirate survivors to complicate matters. Adventurers also have to contend with foul air and other such space phenomenon.

    The powers of Ravenloft provide the murderoid with the power to create a shield of asteroids to keep adventurers trapped in its domain.

  2. An isolated planetoid in the middle of nowhere riddled with twisting caverns and a tiny colony on the far side. The lord of this domain is an Argos of 16HD!

    The Argos is a real disgusting creature "resembling a giant amoeba... (with one) large central eye... and a hundred lashless, inhuman eyes and many sharp-toothed mouths".

    It roams around the caverns and has somehow frightened a small tribe of goblins (that crash landed on the planet many years ago) into worshipping it. The goblins live in the twisting caverns and emerge on the surface to attack the tiny colony of elves and humans that was recently set up as a waystation.

    The powers of Ravenloft provide the Argos the power to foul all air around any creature, ship, or object which will require. Since the planetoid is isolated, the adventurers have no choice but to return to the planetoid.

  3. Another planetoid but this time with five tribes of scros. The lord of the domain is a scro lich that lives in a crypt. Yikes!!! (It should be an interesting story for you to concoct how a militaristic scro could become a lich...)

    The tribes fight with each other to hone their battle skills... When a ship is spotted, they will swarm out in their ships to surround and harrass it. Any captives are made to work as slaves to plant fungus foods in the hilly plains found throughout the planetoid.

    Imagine what happens when elves are spotted by the scro... Ultimate Pandemonium!!!

    The powers of Ravenloft provide the lord to fill the space around the domain with a cold mist... No matter which direction is taken, the adventurers are forced to return to the planetoid.

  4. A disc-shaped planet with three huge mountains strangely spaced equally apart. All the mountains have complex cavern systems. Within one of them can be found the lord of this domain - a noble Patriach Grell...

    Surrounded by the mountains is an ocean and several towns of humans and halflings. Within two of the mountains are towns of dwarves. The races used to be experts in spelljamming but since the domain entered Ravenloft... they just simply lost hope... To worsen matters, the dwarves have completely withdrawn into their towns and make no further contact with the other surface towns.

    The grells have been relentlessly attacking the surface towns... the Patriach Grell is collecting the brains of the surface dwellers for a macabre ritual... Yucks... If only, the dwarves can be contacted to fight back... You know the old adage... United we stand...

    When adventurers attempt to leave... the lord of the domain blasts them with waves of despair that will force them to turn back...