Our fanart Harry Potter Expecto Patronum Deer Sticker features a well-known spell from the Harry Potter series created by J.K. Rowling. It is a defensive charm used to repel Dementors, dark creatures that feed on happiness and can cause despair and sadness. The spell is primarily used to conjure a Patronus, a material form of positive energy, or a guardian that takes the shape of an animal. The Patronus serves as a shield against Dementors, driving them away and protecting the caster and others nearby.