A cool and fun concept. Digging upgrading making progress is a fine loop. There is always the feeling that what pops up on the screen motivates the player to change course. What I found to be rather difficult was the airbourne controls. Sometimes I shot up walls wasting no stamina at all and other times I felt like I couldnt crawl at all. Waiting for stamina when you dig straigth down and try to get back up is really frustrating. Stone is OP, Iron is UP. I would love to see an upgrade that increases the stamina regneration rate. Overall very stable game!