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
Use a Weasley box with every Weasley
Unlock every bad wizard (Single Player Only)
Unlock every character with a pet (Single Player Only)
Unlock all of the members of Dumbledore's Army (Single Player Only)
Unlock every pyjama character variant (Single Player Only)
Unlock ALL of the Order of the Phoenix character variants (Single Player Only)
Unlock all witch characters (Single Player Only)
Defeat 30 Red Caps
Complete the Bonus Level
Defeat Bellatrix with Neville (Waiter) in a duel
Use a Quibbler dispenser 25 times
Unlocked on hitting 50% game completion (Single Player Only)
Complete "Dark Times"
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 "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 "A Veiled Threat"
Complete Year 5
Defeat Bellatrix as any Sirius Black character variant in a duel
Complete "A Giant Virtuoso"
Complete "Kreacher Discomforts"
Complete "Dumbledore's Army"
Collect 1 billion studs (Single Player Only)
Defeat Quirrell in the Quirrell boss fight, using Voldemort
Defeat Harry (as Voldemort), in the Graveyard
Complete the game to 100%
Buy every version of Voldemort (Quirrell/Tom Riddle/Voldemort)
Collect all of the Gold Bricks
Rescue all students in peril
Turn the sound down to 0 and music off in the options menu whilst in the library
Defeat 10 enemies with a Muggle character
Freeze 20 characters using Glacius
Scare 20 students using a ghost character
Defeat the mountain troll, using Quirrell
Complete the Quidditch level within five minutes
Defeat 20 enemies with Fang
Defeat 20 spiders with Ron
Destroy 50 Devil's Snare plants
Buy the entire Weasley family
Buy the entire Gryffindor Quidditch team from Book One
Collect all of the Red Bricks
Collect all of the house crests in Year 4
Get True Wizard in every level
Complete the Story Levels in all four years
Complete Year Four Story Levels
Collect all of the house crests in Year 3
Unlock all Animagi
Collect all of the house crests in Year 2
Hide in a barrel as Snape
Collect 10 million studs in one level
Collect all of the house crests in Year 1
Complete All Story Lessons
Use the Time-Turner
Complete Year Three Story Levels
Complete Year Two Story Levels
Complete Year One Story Levels
Complete all the LEGO Builder tutorial levels.
Knock over ten characters using a ride-able object
Collect 500 ghost studs