The Patronus charm is one of the most difficult spells to master in the wizarding world of Harry Potter. The fact that Harry learns to produce this charm -- moreover, a corporeal form, which is even more difficult -- at just 13 years old shows just how powerful he is. Like many things in the wizarding world, the form one's Patronus takes can say a lot about the magic user.
Source：https://www.cbr.com/weirdest-patronus-forms/
