Thanks for playing! I took a deep dive into experimenting with shaders so I'm glad you enjoyed the results! I kind of lost sight of the 3-hour time limit and just wanted to explore it as much as I could since I was feeling inspired the 2nd day.
For the custom cursor —I'm not sure if it's a new feature for 4.1, but for me it is found in Project Settings > Display > Mouse Cursor. You can even change it during runtime with this:
var arrow = load("res://custom_arrow.png")
Input.set_custom_mouse_cursor(arrow)