Hippogriffs and centaurs, veela and grindylows, unicorns and basilisks ― thanks to J.K. Rowling and “Harry Potter,” mythical beasts like these have become familiar to millions. When he discovers he’s a wizard, Harry is swept off to a school where he learns about these fantastical creatures, as well as magical herbs and powerful potions gleaned from old scrolls of parchment and a library packed with yellowing old books. But Rowling didn’t originally invent most of the magical beings and blooms in her books.