☛ Click the green flag to start the animation. ☛ Click the backdrop to change it. Version 2 is here: https://scratch.mit.edu/projects/1147313110/
This is a very simple way of creating the appearance of a dynamically reshaping rectangle using an overlay and movement blocks. The movement is restricted by the overlay, but multiple overlays could be used to bypass that to some extent. I got the idea for this when working on "Text Color Mystery Explained". The idea was to use it for a text container, but I ended up not using it. For best results, use a rectangle with a solid fill.