Here is the full list of all 17 Grey Area achievements.
Found a hidden level
Found some pizza to look at
Travelled very deep...
Went for a slide!
Completed an orbit
Collected all items in chapter 1
Collected all items in chapter 2
Collected all items in chapter 3
Collected all items in chapter 4
Collected all items in chapters 5 and 6
Beat the game in Punished Mode
Beat the game in Painful Mode
Beat the game in Standard Mode
Beat the game in Relaxed Mode
Broke the fabric of reality
[ACHIEVEMENT_DESCRIPTION]
Filled every pocket of the backpack