The magical dust from the very pouch of the Dream King himself, Dream Sand as a hallucinogen that makes hallucinations real – and makes reality hallucinatory. A user of Dream Sand can mutate the flesh of anyone near enough (and it’s unclear how close that is, although line of sight seems likely), can entrap others in dreams and can prolong their own life far beyond any need for other sustenance (although not without considerable physical wasting – the magic keeps the body alive without them, but the body still needs food and drink).
Fortunately, Dream Sand is kept tightly controlled by the Dream King (whether that be Morpheus or Daniel), and it is only in rare circumstances that any human gets the chance to become addicted to it. The 72 year long imprisonment of the Dream King for the Magus Burgess was such an occasion, unfortunately, claiming the lives of at least two people and very likely more.