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