game mechanics are not what Ravenloft is about.
It's very hard to do a Ravenloft game, it's not the usual at all, and many folk can't play that: to let themselves get scared and concerned.
Characters should get driven mad with fear, horror and do odd things at times: they do it in real life! And it's a trope of most fantasy too.
The undead would scare the bejeezuz out of you. Even the "Romero" zombie films make a crucial mistake in that lane, though they do hit on the fear of a relenetless, unceasing enemy.
A dragon would scare you badly, imagine fighting an intelligent flying tyranosaur!!! Yikes!
That's "fear" and folk can just break down from that at times, no matter how brave they are.
But...something that could condmen you to eternal unlife, not merely to kill you, but make it so you are in unnatural torment forever, a thing that that reeks of of "wrongness"....yeah, that's something else again. That's fear deluxe and it could strike horror into you.
D&D characters are more used to undead, as "real things", so less chance of horror, but still...
DM's law trumps game rules. That goes for Ravenloft. Things do not have to work 100% normally.
the sheer fact that things
don't work right,
is part of the horror.
"You pull your sword from it's sheath, commanding it to burn with fire that will sear your unholy enemy!...But instead, it drips greasy, stinking lard, writhing with squirming maggots!"
(sword now does necrotic damage instead of fire)
Now that will start making players get the creeps!
the dark powers should rarely get involved with players, provided they stick to a moral course. That's part of the threat of Ravenloft.
Dark Sun has thirst; Planescape had will power and philosophy, Spelljammer had the vastness of space, as threats and major items. In Ravenloft, if you go the "easy" path, you may well end upbecoming a permanent denizen...