Sneaking and Hiding NPCs?

[merb]

It would be possible, but it'd take watcher mobs or something of that sort.

For example, you could place an invisible watcher mob at the entrance to a cave with a proximity set so that when a player gets close enough, a mob will spawn and probably emote or shout something.

I'm no quest expert, so I'm not too sure how to set up proximity signals on mobs, but I've seen things like that done before.