Poor Coill normal gets no love. :x
The giant headless at the end of the dungeon can drop a volume beret pattern. :o The lightning sprites can drop TH2, the ice sprites can drop IS5, and the mimics can drop IS3. The sprites and mimics are hardly unique to Coill, but I don't remember any place where the sprites spawns in nice groups like they do in Coill.
Mind, if someone's running this dungeon for money, there are better alternatives, but there can be reasons for people to run Coill. : P