Item scaling is harshly limited by hardware. I might add more steps for getting smaller with distance, but they simply cannot scale up, because of the sprite budget. That's why they circle in midair. The circle scales very well. If you see a tight little orbit, run to it.
Dropoff edges have distinct tiles, where any flat space ends. They're not pretty but they're there. The larger hurdle for platforming is that you can't look down. But if you're holding A, the fall speed is low enough that you can walk off a platform, and then back up back onto it.
The buzz has been fixed! Badly. The sound hardware needs 17 bytes somewhere in 0xC000, and it needs them aligned on 64. If cc65 has a sane way to place data at a specific address, then anybody who knows is keeping it a secret. Some function that happens to be in-range has to smuggle in eighty-one zeroes in a row... as instructions. Constant data is separated. So there's eighty-one BRK instructions, 0x00. Which I then manually locate in the output ROM, to change which address I write to the audio chip.
Some parts of this project feel ingenious. Other parts are dumb as hell.