There is a "dungeon" in Flitwick's Wingardium Leviosa room, under a trap door with a largeshiny lock (You need Reducto to open it, which you don't access until year 4). When you jump in, you can get some loot (bring a Dark Magic user) -- but then you are seemingly trapped. Using Hermione, make your active spell Crookshanks. Then, go to the left top corner and jump out of the window while tapping the spell button. When it works, Crookshanks will appear in the classroom and you can walk out of the room. It takes a couple tries and you will probably kill Hermione several times, but it will work.
Go to the room were you make the old man potion in year four, then go through the door to the right. In the room there is a gate with three locks on it, as well as the three keys. To get the keys, you will need Hermione, Griphook, and a Hufflepuff student (you can also use Dumbledore). To get the first key, go near the door where there's a picture with a man in it and wave to the picture with the Hufflepuff student or Dumbledore. Obtain the second key by making Griphook turn the key on the giant snake statue, which will move and drop the key out of its mouth. To get the third key, you need Hermione to copy the pattern on the bookshelf. Once you have put the keys into the gate, it will open and show some Lego bricks. Move the bricks to make stairs (going to the left). Once done, go up and walk to the far left to find an open chest with Professor Snapes character token.
ACHIEVEMENT - HOW TO UNLOCK Junior (50 points) - Complete Year One Story Levels. Senior (50 points) - Complete Year Two Story Levels. Prefect (50 points) - Complete Year Three Story Levels. Head Boy (50 points) - Complete Year Four Story Levels. Teacher's pet (70 points) - Complete All Story Lessons (Single Player Only). Story Complete! (70 points) - Complete the Story Levels in all four years. Crest Collector (30 points) - Collect all of the house crests in Year 1 (Single Player Only). Crest Fanatic (30 points) - Collect all of the house crests in Year 2 (Single Player Only). Ultra Collector (30 points) - Collect all of the house crests in Year 3 (Single Player Only). The Ultimate Collector (30 points) - Collect all of the house crests in Year 4 (Single Player Only). Power Up! (45 points) - Collect all of the Red Bricks (Single Player Only). The Bonus Level is Yours (70 points) - Collect all of the Gold Bricks (Single Player Only). Student Rescue (45 points) - Rescue all students in peril (Single Player Only). Stud Magnet (30 points) - Get True Wizard in every level (Single Player Only). You're the Best (70 points) - Complete the game to 100% (Single Player Only). Dark Wizards (10 points) - Buy every version of Voldemort (Quirrell/Tom Riddle/Voldemort) (Single Player Only). Quidditch Team (10 points) - Buy the entire Gryffindor Quidditch team from Book One (Single Player Only). Back in Time (10 points) - Use the Time-Turner. Building Blocks (30 points) - Complete all the LEGO Builder tutorial levels (Single Player Only). Good Dog (10 points) - Defeat 20 enemies with Fang. Wonderful Weasleys (10 points) - Buy the entire Weasley family (Single Player Only). Quirrell Quandary (15 points) - Defeat Quirrell in the Quirrell boss fight, using Voldemort. Multiplier (10 points) - Collect 10 million studs in one level (Single Player Only). Arachnophobic (10 points) - Defeat 20 spiders with Ron. Chilled out (10 points) - Freeze 20 characters using Glacius. Boo! (10 points) - Scare 20 students using a ghost character. Animagus (10 points) - Unlock all Animagi (Single Player Only). Defeating the Object (15 points) - Defeat the mountain troll, using Quirrell. Watch Out! (15 points) - Knock over ten characters using a ride-able object. Solid Snape (15 points) - Hide in a barrel as Snape. Role Reversal (15 points) - Defeat Harry (as Voldemort), in the Graveyard. Quiet Please! (15 points) - Turn the sound and music down to 0 in the options menu whilst in the library . Muggle Trouble (15 points) - Defeat 10 enemies with a Muggle character. Lumos Solem (15 points) - Destroy 50 Devil's Snare plants. Quick Quidditch (15 points) - Complete the Quidditch level within five minutes. Ghostly Treasure (15 points) - Collect 500 ghost studs.
If you bought and used the "Christmas" extra, the room you use it in will keep playing the same music for the rest of the game. Similar to the red-haired Ron cheat, it will not revert back to its regular music.
If you get stuck in the Dragon room due to a glitch, resolve it with the following work-around: Play as Hermione and choose her cat on the spell wheel, then head over to the far left corner. Jumping into this corner will kill your character. However, while jumping into the corner, rapidly tap the "release pet" button. It may take several attempts but the pet will appear in the lesson room above. From here, the player can leave the lesson room and continue the game.
After the Leaky Cauldron hub area is unlocked, enter Wiseacres Wizarding Supplies in Diagon Alley before starting actual game play. Go upstairs and talk to the vendor, then enter one of the following passwords to activate the corresponding cheat:
To destroy objects with red sparkles around them, use Dark Magic. To use dark magic, you need to use the Polyjuice Potion or use an evil character in Freeplay mode. An evil characters' Wingardium Leviosa spell is changed to the Crucio Curse and can destroy the red sparkling objects.
Find, post, and buy the "Collect Ghost Studs" extra. The parcel was either in Harry's bedroom or on the courtyard fountain (You must have learned the Leviosa spell first). Once activated, the Ghost Studs are worth 1,000 each. "Get lost" the ghost will return to you and lay more studs, resulting in easy money. A full trip from the Dorm to the Great Hall is worth about 100,000.
Complete the first two levels and enter the wizard town through the Leaky Cauldron. Enter the last shop on the left (before the bank) and buy the "Multicorfors" spell. Cast it on Ron Weasley. Although he shakes his head as if the spell has worn off, his hair will remain red.