Fun game! Graphics were super cute. One observation I had was that the game seemed to be too easy. I played through 5 levels or so and never ran low on air. Maybe scale faster?
Also, I never found a reason to have to dig through rocks. Maybe have spawn patterns were rocks surround an air canister? Or maybe just have more levels of dirt hardness, where part of the game is having to make judgments over which path is fastest based on the different hardnesses.