Full list of all 84 LEGO Harry Potter Collection achievements worth 2,000 gamerscore. It takes around 40-50 hours to unlock all of the achievements on Xbox One.
Achievements they've won
Achievements they've not won
Complete the game to 100% (Single Player Only)
Defeat every Harry freeplay variant as Lord Voldemort
Unlock ALL of the Order of the Phoenix character variants (Single Player Only)
Unlock every pyjama character variant (Single Player Only)
Unlock every character with a pet (Single Player Only)
Unlock all witch characters (Single Player Only)
Unlock every bad wizard (Single Player Only)
Unlock all of the members of Dumbledore's Army (Single Player Only)
Use a Weasley box with every Weasley
Defeat 30 Red Caps
Complete the Bonus Level
Collect 1 billion studs (Single Player Only)
Defeat Bellatrix with Neville (Waiter) in a duel
Complete "The Flaw in the Plan"
Complete Year 8
Complete "Snape's Tears"
Complete "Fiendfyre Frenzy"
Complete "Burning Bridges"
Unlocked on hitting 50% game completion (Single Player Only)
Complete "Back to School"
Complete "The Thief's Downfall"
Complete Year 7
Complete "Lovegood's Lunacy"
Complete "Sword and Locket"
Complete "In Grave Danger"
Visit the Hogwarts Foyer in Year 7/8
Complete the scene where Hermione and Harry dance in the tent
Complete "Magic is Might"
Complete all lessons (Single Player Only)
Complete "The Seven Harrys"
Use the Deluminator
Complete "Horcrux and the Hand"
Complete Year 6
Complete "Felix Felicis"
Complete "Love Hurts"
Complete "A Not So Merry Christmas"
Complete "Just Desserts"
Complete "Out of Retirement"
Complete Year 5
Complete "A Veiled Threat"
Defeat Bellatrix as any Sirius Black character variant in a duel
Complete "A Giant Virtuoso"
Complete "Kreacher Discomforts"
Complete "Dumbledore's Army"
Use a Quibbler dispenser 25 times
Complete "Dark Times"
Complete the Quidditch level within five minutes
Defeat 10 enemies with a Muggle character
Defeat Harry (as Voldemort), in the Graveyard
Defeat the mountain troll, using Quirrell
Scare 20 students using a ghost character
Defeat Quirrell in the Quirrell boss fight, using Voldemort
Defeat 20 enemies with Fang
Freeze 20 characters using Glacius
Complete the game to 100%
Buy every version of Voldemort (Quirrell/Tom Riddle/Voldemort)
Complete all the LEGO Builder tutorial levels.
Collect all of the Gold Bricks
Collect 10 million studs in one level
Unlock all Animagi
Buy the entire Weasley family
Buy the entire Gryffindor Quidditch team from Book One
Collect all of the Red Bricks
Rescue all students in peril
Turn the sound down to 0 and music off in the options menu whilst in the library
Collect all of the house crests in Year 4
Get True Wizard in every level
Collect all of the house crests in Year 3
Collect all of the house crests in Year 2
Collect all of the house crests in Year 1
Destroy 50 Devil's Snare plants
Hide in a barrel as Snape
Use the Time-Turner
Complete the Story Levels in all four years
Complete Year Four Story Levels
Complete All Story Lessons
Complete Year Three Story Levels
Complete Year Two Story Levels
Defeat 20 spiders with Ron
Knock over ten characters using a ride-able object
Complete Year One Story Levels
Collect 500 ghost studs