Huh, that's a pretty creative mechanic! Solved everything except for level 9, which I'm too tired for today, and I'm very sure I cheesed level 12. I couldn't figure out if there were deterministic rules which direction a push would happen when a block would grow from both sides? Probably there are, but they weren't super clear. I think mechanically, making that more intuitive is the biggest challenge. After that, add some more polish and a couple more levels and you've got a good puzzle game ready to ship :D