Just replace the costume with your thumbnail, and whenever you click the green flag, there will be no thumbnail, and when the stop button is pressed, the thumbnail will glide down smoothly. This project uses the timer to check when the stop button is pressed. WARNING: If your project uses the timer in any other aspect, this might interfere with it.
YouTube Tutorial for this: https://youtu.be/INPasr9FyW0 Thanks to @rehanscratch for using this so I could understand the basics and recreate it.
