Lego Harry Potter year 1-4

After riding the lift up, you'll be in a room with a crate on the right. Destroy it and a bludger will come out. When you see red circles appear around you, it means that it's locked on to you. You can use this to your advantage to create a ramp: stand in front of the pillar holding up the raised platform. Stay still. When you see it lock on to you, move out of the way. The bludger will destroy the pillar and a ramp will be created. Head up it.

On this raised platform destroy the bludger chest. Again, use it to destroy the pillar to create another ramp for you. Head up and then climb up the ladder to end the level.