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