For the blocks you should put the block in editor of Snap! then do script pic and import it as a costume for the block in mini. Also he/they
Also some graphics could be improved. You could make your own categories tabs in a vector so that it is not as blurry.
We could also use my version and resize the stage on my version and add categories. I think it will be better if we do it that way since Snap! Build Your Own Blocks has the connections system, block graphics, and flag/pause stuff. It also has the run system nailed. For the version in my possession we could add sprite creation and selection at the bottom.