Here is the full list of all 50 The LEGO Movie 2 Videogame achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Do a build attack
Open a Discovery Chest
Unlock Lucy
Complete the Apocalypseburg Level
Defeat the Apocalypseburg Boss
Collect All Master Pieces on Apocalypseburg
Complete the Asteroid Field Level
Collect all Master Pieces in the Asteroid Field
Complete the Systarian Jungle Level
Defeat the Systarian Jungle Boss
Collect all Master Pieces in the Systarian Jungle
Complete the Harmony City Level
Collect all Master Pieces in Harmony City
Complete the Sorting Area Level
Defeat the Sorting Area Boss
Collect all Master Pieces in the Sorting Area
Complete The Ceremony Level
Collect all Master Pieces in The Ceremony
Complete Classic Bricksburg
Collect all Master Pieces in Classic Bricksburg
Complete the Old West
Collect all Master Pieces in the Old West
Complete Middle Zealand
Collect all Master Pieces in Middle Zealand
Complete Planet Unikitty
Collect all Master Pieces on Planet Unikitty
Complete the Planet Sparkles Level
Collect all Master Pieces on Planet Sparkles
Complete the Main Story
Unlock Rex
Unlock Unikitty
Unlock MetalBeard
Unlock Benny
Unlock Batman
Unlock Sweet Mayhem
Unlock a Gold Character Variant
Complete the Syspocalypstar Sandbox Tutorial
Build 20 Buildings in Syspocalypstar
Collect 1000 Brick Pickups
Collect 100 Items in the Game
Collect 100 Characters in the Game
Open your First Relic
Open 50 Relics
Play as a Minidoll for the First Time
Buy Something in a Shop
Open your first duplicate relic
Complete the Game to 100%
Collect 1,000,000 Studs
Shoot 50 Stickers with the Sticker Gun
Try and place an object somewhere you can't, while on Syspocalypstar.