After you defeat the Gytrash, there will be an intermission sequence with Quirrel. Here, you will first see Voldemort. The battle will begin when he uses Wingardium Leviosa. The entire battle is worthless. You can even defeat him without being hit once. There are two parts to this battle. This part is optional, but very helpful. Run behind a pillar that holds the ball the Voldemort uses Wingardium Leviosa on. Voldemort will follow you and begins to cast the red spell. Immediately as he fires the spell (when it comes out of his wand), run away from the pillar. The spell will hit the pillar and destroy it. Repeat this with the other pillars so he cannot use Wingardium Leviosa on you. In the required "real" battle, run in front of the mirror to where your parents are protecting you with the white band. The goal is to reflect the spell at Voldemort (as instructed by the intermission sequence). Let him cast the red spell at you. You will turn green, then the green fades to white. The remote will begin to shake. When you are fully surrounded by white, face Voldemort and press X. The spell will shoot at Voldemort. This hurts him a lot. Repeat this until Voldemort is gone, then enjoy the intermission sequence. You wake up the next day in your dormitory. There will be an intermission sequence with Dumbledore. After that, go to the Great Hall. Take advantage of the last day. Do not enter the hall because this is the final area and you cannot save the game once you enter it. Explore the school and get all the Wizard Cards, etc. Then, enter the hall for a final intermission sequence, and the award for the House Cup.