This addon to Griffpatch's Super Mario Advance 4 engine makes some adjustments to slopes, adds sliding down slopes, and kicking Goombas while sliding. I also fixed one of my issues with this project, which was the way that Mario skids when crouching even if he's in the air. Now, I don't think this is a perfect implementation of sliding, and I'm not sure if its accurate to the sliding physics of Super Mario Bros. 3 or Adv. 4. Feel free to mention any inconsistencies between this project and the games, or any way to make the code more efficient.
This project is an addon to Griffpatch's Tile Scroller Tutorial (Episode 16 Scripts): https://scratch.mit.edu/projects/572484485/ To make use of this project, simply backpack the Mario sprite and the Enemies sprite and use them in place of the sprites in the original project. Keep in mind that these are the episode 16 scripts, and you'll have to update it from there. If you've already completed the scripts up to the latest episodes, it may be easier to mix and match the new scripts into your original Mario and Enemies sprites. You'll need to have the shellkick sound in the Enemies sprite for my implementation to work.