I would probably have to say mostly the rocks and the pickaxe.
I had trouble with the collision between the two, and the rock's respawn was really hard too. Josiah had to help me with that one.
Miner Life wasn't really suppose to have a story. I wanted it to be like a sandbox in a way. My teaser I drew almost a month ago is about a game I will make that will have a story. So don't you worry. :D