The jam doesn’t allow sprites,
Oh? I thought it was external sprites. If you poke a sprite in from the 560 chars of code is it still not allowed?
I don’t even know yet if that’s plausible to do in 560 chars, but I was going to try it at least once. I was going to try OP’s 1-pixel sprite example then realized there’s no advantage to doing so for a single pixel in Tic-80.