What does the little checkbox that says “run without screen refresh” do when making a custom block? I know it's used in blocks that relate to games and projects of that sort because I've seen video tutorials of people using the feature but when I used it in my animation code it broke the code and didn't work.

Like it says, it runs without refreshing the screen. Games use it since certain functions need to be running without the screen refreshing since otherwise it would be extremely laggy. Animations on the other hand work by having the screen refresh so using that checkbox is not the best idea for animations.

Ok thanks!