The Collector (Important) wants 1 Wildfire Stone and 1 Blizzard Stone
It sounds simple, but it requires going in/out of dungeons constantly possible for hours at a time to get the stone drops from the radar treasure chests, and they are uncommon at best, you mostly get sprouts or other useless junk and to add insult to further injury you require 5 of each - this heavily slows up the game and adds a huge amount of frustration and boredom