The Harry Potter series is full of mystical creatures and beasts, many of whom are important to Harry's journey in some way. The Fantastic Beasts and Where To Find Them book (and the subsequent movie series) outlined some of those creatures, from Unicorns and Bowtruckles to Nifflers and Thestrals. Hippogriffs also feature heavily in the series, particularly Buckbeak, who becomes a companion of Harry and company. A lot of times, each subsequent book will feature a new creature that hasn't yet been introduced, and Hogwarts even has a whole class called Care of Magical Creatures, taught by the beloved Hagrid, that is dedicated to educating students on these magical beasts.