Instructions
Play through the game's story mode until you reach Level 3 of Year 4. In this level, you'll get a new spell, Reducto. Select Reducto from the spell menu and then use it to destroy all the marked targets. Once you complete the level, you can use Reducto in any other area of Hogwarts.
Go downstairs to the fourth floor of Hogwarts. Head west and enter the Charms classroom at the end of the hall.
Use the Reducto spell to destroy the silver lock on the left side of the classroom. Go through the door to access a secret room.
Break the two orbs in front of the dragon with Reducto.
Hold down the "B" button to reassemble the broken dragon if you're playing on the Wii. On Xbox 360, hold down the "X" button. On PlayStation 3, hold down "Square." Once you repair the dragon, you earn the Mad-Eye Moody character token.
Jump on the dragon's head when you're ready to leave the room. The dragon will lift you up and out of the basement. You'll collect a gold brick on the way back up.