Instructions
Play up to Year 4, Level 3: "The First Task" in story mode. You will need to know the spell "Reducto" to unlock Tom Riddle. You will automatically learn this spell in story mode after you play Year 4, Level 2: "Dragons" and complete the "Reducto" lesson before Year 4, Level 3 begins.
Find the character token for Griphook. You must unlock Griphook in free play mode before you can unlock Tom Riddle. The Griphook character token is in Year 1, Level 1: "The Magic Begins." Play this level on free play with any character who can use the "Reducto" spell. Make your way to the final room of the area, the room filled with locked vaults. Use "Reducto" on the shiny treasure chest with a lock. Grab the Griphook character token.
Purchase Griphook from Madam Malkin's Robes shop in Diagon Alley between levels to unlock him. Griphook costs 55,000 Lego studs.
Play as Griphook in Year 2, Level 6: "The Basilisk" free play. Select Griphook and make your way to the final room in the level, where you battle the Basilisk. Locate the vault with a key toward the back right side of the room. Stand in front of the vault as Griphook and open the vault. You will find the Tom Riddle character token inside.
Buy the Tom Riddle character token from Madam Malkin's Robes shop in Diagon Alley between levels to unlock him. Tom Riddle costs 85,500 Lego studs.