Here is the full list of all 15 Constant C achievements.
While free-falling in high speed change the direction of the gravity and apply brakes
Complete story mode
Gather all storage devices
Found the dinosaur
Discover the phone-microwave
Complete all levels for chasing Ellie 2.0
The total number of deaths exceed 150
Reach the storage device location in D3-3 and safely pass the level without dying
Change the direction of gravity while in the midair at least 10 times and land safely
Gather any storage device inside the 6th portal without using the second time field
Pass C2-2 in 5 seconds
Pass C3-3 in 5 seconds
Pass C3-4 in 7 seconds
Pass F1-5 in 20 seconds
Pass D1-5 without falling off the ball unnecessarily