You earn this achievement by opening 50 of the cubes that pop open and give you oxygen, power, or an upgrade (?).
To open a cube, go up to it and press
. It's up to RNG for whether or not it pops open. You can keep trying though.
I was still missing this at the end of the game, so I went back to the first level.
There was a cube over to the left of the hill from spawn, so I went and popped it open and waited for my achievement percentage to increase.
I don't believe that the cubes respawn, so I used the method from this guide for Blast 'em Bunnies (
skip to about 1:10) just to make sure that I could repeatedly get the same cube.
Repeat until you reach 50