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