Originally posted by Nerevar:

same as rancid remains enemy. which is also very rare to be encountered at all. yet has a unique trophy. but thats about it.

i still dont get why enemies in dungeons never respawn. seems like a similar mistake as the forest.

I guess once the dungeons are looted, you don't have much of a reason to go back down there. Its not like the enemies are worth farming in any capacity either.
Rancid Remains spawning in swamps after Bonemass would be cool, but at least they appear in the Skeleton Surprise event. The poor Ghost is so underused for how neat it is, doesn't even have a trophy.