The Patronus is the most famous defensive charm. The aim is to produce a protector, which takes the form of an animal. The exact form of the Patronus will not be apparent until the spell has been successfully cast. It is the only spell effective against Dementors. The majority of witches and wizards are unable to produce Patronuses and to do so is generally considered a mark of superior magical ability.Since he had last seen it, the gargoyle guarding the entrance to the headmaster’s study had been knocked aside; it stood lopsided, looking a little punch-drunk, and Harry wondered whether it would be able to distinguish passwords anymore.They clambered over him and onto the spiral stone staircase that moved slowly upward like an escalator. Harry pushed open the door at the top.He had one, brief glimpse of the stone Pensieve on the desk where he had left it, and then an earsplitting noise made him cry out, thinking of curses and returning Death Eaters and the rebirth of Voldemort.I need the place where everything is hidden, Harry begged of it inside his head, and the door materialized on their third run past.I’m putting the Elder Wand, back where it came from. It can stay there. If I die a natural death like Ignotus, its power will be broken, won’t it? The previous master will never have been defeated. That’ll be the end of it.