You've got me thinking of all my past projects and what the first bosses were like. I'd have to say just a part of the story, better stats. I've since looked into a little more and I think that I still have them remain a big part of the story, and those higher stats, but challenging the player or introducing something else that may be coming up. A way to foreshadow things. Whether mechanics, a new set of items, maybe a level with puzzles and just little nods to it.