In the Harry Potter series, the rarest magical creature is generally considered to be the Phoenix. Phoenixes are known for their ability to be reborn from their own ashes, making them extremely rare and powerful creatures in the wizarding world.
Elder. The rarest wand wood of all, and reputed to be deeply unlucky, the elder wand is trickier to master than any other. It contains powerful magic, but scorns to remain with any owner who is not the superior of his or her company; it takes a remarkable wizard to keep the elder wand for any length of time.
