In Sorcerer’s Stone, we hear that Fred and George are throwing snowballs at the back of Professor Quirrel’s turban. Since we later learned that Lord Voldemort was hiding out in Quirrel’s head, that means our merry Weasley pranksters were embarrassing the darkest of dark wizards.’
I remember being sure when I first cracked Deathly Hallows that Hagrid was done for. But Rowling wanted so much to see Hagrid walking out of the Forbidden Forest with Harry’s pseudo-lifeless body that his death was never seriously considered.
A deep love for the school inspired Tom Riddle to find relics important to the four founders of Hogwarts and turn them into his Horcruxes. While he got Ravenclaw’s Diadem, Hufflepuff’s cup, and Slytherin’s locket, we were lead to believe that Lord Voldemort never turned anything of Gryffindor’s into a Horcrux.
But that turned out to be only kind of true, as Harry himself, the Horcrux Voldemort never intended to make, was not only a descendant of Gryffindor’s, but was so true a Gryffindor he pulled the man’s sword out of the Sorting Hat. At the end of the day, Voldemort completed the set, which, for any collector, is way more important than ensuring one part of that set doesn’t kill you.