The big fun Change I made was adding reversed gravity to every 3rd Shot. Because it can happen that the tiles of the Castle block the goal and if you have reversed gravity you are able to get your ball underneath it or kick them away. I felt like its a fun change and the first time you play it is fun to see the reactions of the people who try to beat the level.
I added a plop Sound to the Slingshot. I would have loved to add a sound to the flying projectile but I could not find or make a sound I was satisfied with.