you use your finger / mouse to draw to change size to 20 click paint brush to change size by 40 click highlighter. WARNING: if you change thickness half way through a drawing it will delete, i really can't be bothered to fix that. and also it can only reach a certain amount of pixels and it stops.
i came up with this myself. All by @Addie098876 WARNING: you only have a certain amount of pixels as there is only 300 clones the sprite can make!