I tried to optimize it, but I was testing my optimizations on a gaming laptop which made it hard to see what made a difference (T^T)

The dark wall around the edge is just a border to keep the player in. I guess in a game all about destruction, it's hard to show what the player can't destroy.

If you were referring to the stone bricks, yes you can destroy them, it just takes a while.

This almost caused me problems :/

The fire attack looked way cooler so it was all people were using initially. I had to add help text to say that you couldn't burn down a rock wall eventually D: