it's just a mouse trail. i'll try to make a platformer using this mouse trail. If you go into the code and take away "delete this clone" it'll leave parts of the mouse trail everywhere. I also added some triangles, see if you can spot them :D
I used a tutorial to make this and I used the code. The original code is: https://scratch.mit.edu/projects/171044509/ And the username is: @CheriseW