It took me way too long to realize I promised to post the full artwork, so I believe it's better to do it now.
Here it is, a full reference of Mark, my original character. As weird as it might sound, but it was originally created as a temporary fursona replacement (art of which I'm still planning to get one day) . But since I only have the black monster for now, I decided to keep him as an OC. To tell the truth, I don't regret it at all.

Compared to Dragonsnow's Puro, Mark is more withdrawn and does not want to become human. Unlike other black monsters, he is incapable of transfurring anyone. That's because Mark voluntarily agreed to DNA stabilization, effectively becoming just a fluffy black wolf with white mask. (It's just how I see the explanation of how failed samples work)

Artwork is again done by my friend. And yes, the background of a photo is a window