I played in that module twice. I DMed it once.
In the first game, my 10th level druid Cyndelle (half elven female) ventured into the realm of Ravenloft along with a large group of 1st through 3rd level characters.
You did hear that right: 1st through 3rd level characters. I do not think our DM was being quite reasonable here: nobody had higher level characters but me, and he wanted to run a high level module, but would not allow pre-generated higher level characters. The result was inevitable.
A few things stick out in my mind:
1. The map. Even after I finished the 2nd experience in Castle Ravenloft, and then studied the map as a DM, it took me hours to memorize it, to be able to visualize it in my mind. A nice setup: the family lived in the castle, and their guards and servitors lived in the castle, but the twain never met except through a few, specially designated entryways. In effect, the castle had two completely separate floor plans, intertwined but never actually meeting, spread out over many levels.
Of course, we had a wee bit of difficulty trying to map Castle Ravenloft as players. Indeed, I would daresay it was an epic endeavor. When we had mapped half the castle, the DM asked to see our map. He took a look, got this look on his face, and kindly commented we should throw the map away at once.
After all, our map showed that we had come in a complete circle, and should have been walking into familar territory. And, as you might guess, nothing at all looked familiar.
2. The maid. The words maid and maiden took on a new and terrifying significance for us, because the Castle Maid of Ravenloft - being a vampire - killed half the party. The other half lived, because we ran away.
3. We finally challenged Count Von Strahd to a personal battle. He agreed (we yelled until everything for miles was awakened.) In that final battle, we all died. Only Cyndelle died a natural death, falling from - 3 hit points to - 10. Everyone else, became servitor vampires.
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My second venture into Ravenloft was with Edena (the character, not my SN here.) Edena was a cleric of around 25th level at the time. Cyndelle had been his half sister, and word had finally somehow reached him of her death at Strahd's hands. He went in to avenge her, and to retrieve her body if possible (or, slay the vampire she had become, if that was what was decreed.)
Edena successfully killed Strahd, and it caused the barrier around the realm to temporarily relent, allowing Edena to leave with Cyndelle's body. He then resurrected her.
Edena never did find the bodies of the other adventurers from the first disastrous game, unfortunately.
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I then DMed Castle Ravenloft for someone.
I made the Castle Maid into the spokeswoman for the Count, and she went with his magical carriage to 'invite' the PCs to the Castle. I created a Son of Kyuss (nasty things) as the High Clerist of the Castle (he even sat at the formal dinner engagements!) And Strahd was most happy to welcome and greet the PCs ... and inform them that they were now his servants; loyal servants would be well rewarded, and disloyal servants would be punished.
The angry PCs left the dinner party, then saw the chapel ... in which a holy relic still remained, untouchable by any of it's dark guardians and an eternal reminder to Strahd of his downfall.
The PCs - to my dismay - rushed the chapel (taking the gargoyle and dragon guards by complete surprise) grabbed the relic, then dived through the stained glass windows. Unfortunately, as I had previously stated, Castle Ravenloft sat on a cliff, and it was a several hundred foot drop right beyond the window ... and they had charged through that window blindly, and so could not stop, and ...
Well, I gave them a chance to grab at things, and they did. Strahd did not send his flying minions after them: Strahd was astounded and bemused by this audacity, and determined they would make fine servants indeed, given the proper training and breaking process (sorta like seeing a proud horse, and determining you will break that horse into meekness.)
The PCs, after a mountain climbing type experience, made their escape.
Strahd invited them to dinner again, relic and all. (Strahd was hardly afraid of it, since in his own castle he considered himself supreme.)
This time, all war broke loose.
The party used magical items to kill the Son of Kyuss. They did battle throughout the castle. The Maid evaded them (the Maid, always looked out for Number One first, and her master Strahd second.)
Finally, they killed Strahd in the classic way, stabbing him with a stake while he slept. They cut off his head, put holy waffers in his mouth, the whole kit and kobottle.
And then, the Maid returned and with a Scroll of Undead Resurrection, proceeded to return Strahd to unlife.
Which shows that, in the case of vampires, you need to do the job THROUGHLY, if you are going to do the job at all. Vampires are just too smart, too clever, and have too many contingencies for anything else. Did I mention most of them are mages and/or clerics? That doesn't help matters.
My now VERY frustrated and angry players returned to Castle Ravenloft. They entered through secret lower levels. Then something akin to Total War occurred as they systematically destroyed the place room by room, monster by monster.
They finally got Strahd. This time, they didn't leave anything of him to resurrect (alive or undead.)
And this time, they chased the Maid down ... but the Maid offered an alliance with them against Strahd, if they would free her from his mastery, and they accepted it. Of course, as a result, the breakin of Castle Ravenloft was thus enabled, the overthrow of Strahd and his minions was easier (a vampire helping out is no small thing), and the Maid survived ... to resurrect her master yet again ...