I would really like super rare materials that spawns very rarely but in sort-of big pockets like:
– A metal that only spawn in one specific world and in that world very rarely but where it spawn it spawns maybe 30-50 of it (or enough to make a few items out of it).
– A type of tree that only spawn in cluster of 2-3 and only once
If this sorts of trees/plants/metals exist people could acquirer rare materials only they and a few others have which would make trading of rare materials a big part of the game