So in path of exile there’s a guy that appears randomly somewhere in the game and has one (sometimes) fancy random item.
I think a traveling merchant like that could be a pretty neat addition to the game. It encourages people to roam the world around them. I’m thinking he could recall to random world boss spawn points or anywhere in general, staying at each spot 10-15 min at a time. Until the item is bought on him, a new item won’t appear to be sold. Or you could try killing him, but he’s a blue slaad or something worse where you might need a pack of folks to kill him. His head could then be collected as currency for some other special merchant.