Index · spell · book 3
Expecto Patronum
A shield made from a happy memory, shaped often as an animal, used against dementors.
Expecto Patronum is joy given a job. The caster holds a memory strong enough to push back creatures that feed on cheer. The form is frequently an animal. Fans treat the animal as a personality key. The books are more cautious: the form can surprise the caster, and it can change.
Later the same bright animal can carry a message. A shield becomes a letter. This journal’s Patronus quiz is a parlor game on top of that idea. It does not reveal a canonical form.