This is obtained on the 'A Turn of Events' level. After you defeat Voldemort he will chase you through the castle. To get this you have to destroy less than 10 items while running from him. The objects that slow him down the most are the stone torches, the pillars, and the ceiling. Run past both torches and then as you are running up the second set of stairs shoot the roof down. I made it past this whole section without shooting anything until the first pillar that you can knock down. After this simply shoot at the stone torches and the other pillar and you should be able to do it. If it doesn't unlock during the cutscene quit out and choose continue story. I say quit out because after this cutscene it auto saves and you can't retry it straight away.