Here is the full list of all 38 Pile Up! Box by Box achievements.
Buy every costume
Pick up every collectible in the game
Open the bonus route in Citizen Cave
Complete Feather Theater 100%
Watch a performance by colorful friends
Open the bonus route in Feather Theater
Complete Forest Fair 100%
Watch a fireworks show with spiky friends
Do something horrible...
Open the bonus route in Forest Fair
Explore all of Boxling Square
Watch a movie with upside-down friends
Fall to your doom 100 times
Build an autonomous flying box
Listen to a musical performance by some slimy friends
Make a pile of 5 boxes or more
Open the bonus route in Frogipelago
Put on a new outfit
Bounce a trampoline... on another trampoline
Carry an item through 10 consecutive rooms
Long jump: dash and jump!
Finish the tutorial (no skipping)
Make a pile of 10 boxes or more
Make a very big pile of 20 boxes or more
Throw a pile of 10 or more boxes into the water
Play every game in the arcade
High jump: heavy dash and jump!
Destroy a pile of at least 10 boxes
Finish the game faster than the Seed By Seed record
Scare every spider in the game
Complete a world without falling
Strike a pose on a pedestal
Complete Frogipelago 100%
Open every beach umbrella
Smash every squash in the game at least once
Complete Citizen Cave 100%
Move the wall of boxes in the cave to another room
Unlock all other achievements