Another useful thing you might not know about could be blend modes. I think on medibang it’s above the layers and called “blending.” Most of them you don’t need to worry about, but the most useful one (imo) is multiply. Multiply will make the colors of that layer appear darker on the layers below it, which is useful for making shadows. (It works best when you use a greyish color for the shadows) using this can speed up your rendering process a lot. ^^
