Credo Quest: Black Smith
Craft (random type) sword. Then jam sword into the requested quest giving boulder.
The sword then cannot be removed from the quest giver by anyone (boulder can still be destroyed with enough strength, but otherwise is partly-"magically" protected while having the sword (just to prevent naked hearthlings from breaking this blatant quest giver)).
Credo Quest: Nomad/Wanderer
Pull the sword from the quest giving boulder (assuming there is one with a sword inserted into it, and assuming the sword is still ingrained inside it).
I think this would be pretty neat, there aren't any dynamic quests that involved other players at some point. Since this game is very big on being a persistent open world, I think this would fit.