Like how in climbing, the difficulty goes from beginner to expert, I'd like some PvE quests that are not meant for the general target audience but are hard for those who want a PVE challenge beyond anything else.
The first thing that comes to mind would be parkour which was harder than anything else. Or a more difficult boss in terms of you need to dodge a lot. Or a skeleton fleet of "high-ranking, elite skeletons" that even the better players would need to focus on to beat.
