I made an edit

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First off, it is difficult to shade a ghost, the biggest reason being that they are semi-transparent. It's basically like shading mist. Another reason why shading is difficult is because it is so small, and with small images , the general shape and form is more important than the details. What I did is not to worry about the shading, and just get the form of the ghost down, along with some clothes. Ghosts resemble a person, so I drew a human-like figure first. Then I made it look kind of whithered, after that, I cut down the legs to make them seem like they are fading away. Then I added some clothes on in a different color. I also made it a little bit bigger, just so that I could put in some more detail. So yeah, I hope this helps.