Ravenloft and it's Monsters

[Promethean]

What happens when a creature that gains significant power from contact with the dark powers(fiends, vampires, Villains, PCs, etc.) leaves ravenloft? Do they keep the powers they gained in ravenloft but stop advancing, loose their new abilities, or take a piece of ravenloft with them and keep growing like a cancer in the material plane? Can things that get caught in ravenloft end up in other settings?

Ravenloft as a setting is funny in that unlike other settings, it overlaps every d&d world. It can appear at any time to suck adventurers and convicts in for an adventure before spitting them back out into their own setting. So crashed star-jammers ships, mad red wizards, and an imprisoned dragon overlord can all appear in the setting, and it's even included in the metaplot of editions with the rise of vecna.

The stuff that manages to escape tend to be world changers themselves(vecna, lord soth, the PCs), so it seems like a breeding ground for arch-villains and strange encounters

[DrMotives]

I think the rules don't cover that because the whole point is that escape is nigh impossible, and for a lord of Ravenloft even moreso. Ravenloft is better at its job than Carceri, frankly. Escapes are supposed to be rare enough that they need to be worked out on an individual basis. But, I can see two ways to handle an escaped lord. First, if the lord has really escaped, then all gifts from the mists are gone as well. All gifts and power gained from being a lord are part of the two edged sword of imprisonment. The other possibility is the lord retains power, but that means they also retain the attention of Dark Powers. The Dark Powers will keep watching them, and for the rest of the former lord's life, they need to watch out for misty nights swallowing them back into Ravenloft.

[Promethean]

I think the rules don't cover that because the whole point is that escape is nigh impossible, and for a lord of Ravenloft even moreso. Ravenloft is better at its job than Carceri, frankly. Escapes are supposed to be rare enough that they need to be worked out on an individual basis. But, I can see two ways to handle an escaped lord. First, if the lord has really escaped, then all gifts from the mists are gone as well. All gifts and power gained from being a lord are part of the two edged sword of imprisonment. The other possibility is the lord retains power, but that means they also retain the attention of Dark Powers. The Dark Powers will keep watching them, and for the rest of the former lord's life, they need to watch out for misty nights swallowing them back into Ravenloft.

I didn't really mean the Dark lords in particular. I mean, only two have ever escaped and minus male vistani seer shenanigans the others aren't looking too hopeful. I was more pointing to those who were pulled in with them, the random townsfolk, lesser vampires, and low caste fiends who become sort of mid-bosses of the realm from exposure to the dark powers. They also have a much higher chance of actually escaping.