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