Here is the full list of all 16 In Between achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Complete the game without dying
Watch the credits
There's more than one route to follow.
Find the 5 hidden glimmers of hope.
Complete Acceptance
Complete all levels
Complete five acceptance loops
Complete Depression
Reach all MindImages
Complete Bargaining
Complete Anger
Die 100 times
Complete Denial
Do a successful gravityzone jump
Complete Tutorial
Reach one MindImage