In the making of xy, there are many things none of you ever saw. This is where I'll share them with you.
During the transition between an 8 diameter ball and a 1 diameter ball, I actually had 8 different sprites, all in a row, of ball diameters 1-8. The ln and sto buttons increased/decreased ball diameter on the fly, and - made trails appear at the four corners of the ball. It actually looked pretty cool, but I realized I could never get a collision engine working the way I wanted it to unless I had a ball diameter of 1, so that version was never uploaded.
Also, the very first collision engine had a divide-by-zero error when the ball speed was 0, and it locked up, and I had to do a battery pull. I got thouroughly depressed by that.
I'll share more when I get the chance.