You've made a nice level here! The graphics are extremely accurate; I like the skydome in the background, and I like the fire as moss! The gameplay is great, but the boss is kinda boring. Also, I found a softlock (unless there's a hidden block I missed) here:
If you start from the other side (to the right) and kill the chuck, and then jump back over with the hidden block without breaking the gray bricks under Mario in the screenshot, you can't get back through.
Also also, you can bop the gray bricks with a p-switch which reverts them to turn blocks, but I don't think you can stop that.