Rarest is hard to say. Maybe some of the SRL event ones or the crimson double shaders, as I made sure to get all of those. I also had queen's web and glowhoo shortly after they came out, which were both pretty rare at the time. I'm not sure anymore as both are easily solo'd now. I have all the nm and fwc shaders and some of the DO shaders. No kingspyre yet, and no HM helmet to get ascendant plane. I'm completely unsure.