Instructions
Play through the story until you complete the "Dragons" event during Year 4. When you complete this event, all characters will learn the spell Reducto, which breaks objects apart.
Press "Start" at any time in the game, bringing up a menu. Press "A" on "The Leaky Cauldron," followed by "Yes" to confirm your decision to travel to the Leaky Cauldron. Wait a moment for the level to load.
Walk up to the Free Play board, located near the back of the stairs in the Leaky Cauldron. Select "Follow the Spiders," which is the fifth level of Year 2. Select any character you have unlocked who can use magic, such as Harry Potter or Percy Weasley.
Play through the level until you reach the fight with Aragog. This is a large spider boss fight that occurs in the middle of the level.
Locate the orange chest while you are fighting Aragog. Hold down the "Y" button and select the chest to cast Reducto on it. Destroying the chest gives you the Lucius Malfoy character token, which grants you the right to purchase him in the store.
Press "Start" and select "Save and Exit." Return to Madam Malkins' clothing shop in Diagon Alley where you purchased previous characters.
Purchase Lucius Malfoy, who costs 135,000 studs, which is the in-game currency. Purchasing Lucius Malfoy allows you to play as him during the story mode, and during Free Play mode.