pemerton said:
As someone mentioned on the SoD thread, these sorts of monsters aren't part of the combat system at all. They're part of the exploriation mechanics.
Well, yes and no.
Yes, monsters like this can make up part of the exploration rules -- ear seekers and rust monsters come to mind. "Gotcha!" monsters. Monsters as traps.
No, that's not the only place they should occur. There's a lot of room for monsters that work more like horror villains: they will kill you, and you will not be able to kill them. Perhaps you can survive an encounter with them. Perhaps you will win a victory over them. Perhaps you can find a way to defeat them, however temporarily.
Or even monsters who just work more like a mythic villain: there is a trick to avoiding their doom-causing effect, or but once you know the trick, you can probably kill them without a 10-round slog-fest.
So, while you're right that exploration monsters can have these effects, they can also occur in things that are supposed to be
conflicts but that aren't necessarily supposed to be
combats. When you finally kill the vampire, or the medusa, or whatever, it's over in a flash. The challenge is working up to that point (and pulling off the plan well).
This plays into shorter encounters, and the possibility of balance over the course of the adventure. If the actual fight with the vampire is short and sweet, that leaves a lot of room in the adventure for other types of extended conflict (such as finding its coffin, discovering its weaknesses, etc.)