Tip: Layer 3 backgrounds and tides disappear when you hit a message box, so plan your level around that. For example, you can add a sublevel without layer 3 at the start/midpoint, and include your message there.
Having a bit of trouble getting everything working properly. (Using SA-1 Rom) I've inserted the blocks using GPS and used UberAsmTool to import the code provided, but for whatever reason the switches aren't solid and Mario cannot interact with them, and the blocks are just acting odd in general. Did I miss an important step somewhere? But besides all that, (from the GIF at least) great work! It looks awesome.