Ambergris is legendary for good reason; it's extremely precious, it has a fascinating history, and the scent, as Mandy aptly describes it, is "a beautiful, shimmering amber. It makes everything in the perfume smell better."
Ambergris is actually the intestinal leavings of sperm whales. Aged hunks of it sometimes wash ashore, and people have used it since pharaonic times, when the ancient Egyptians burned it as incense. Banned in the 1970s because sailors were slaughtering sperm whales to extract the stuff from their stomachs, perfumers have been able to use natural, washed-ashore ambergris again since 2005.