Your palette choices are really.... poor. Do you try grayscaling? Its a really good way at checking if your values are nice and readable. It helps you realize when your darks are too dark or when your light are not light enough. If you were to grayscale this for example, you would realize the contrast between the darker blues and even blacks aren't good enough, they blend too much together. I think your expression skills could use some work, I can't tell what expression sonic is giving off in the hurt sprite, is it glee? is it frustration? His mouth looks too much light its giving a grin so he looks happy. I also feel like the closed eyes could be pushed more. Those are the eyes sonic makes when someone eats his chilidogs, not getting punched in the face. I feel artists today are too afraid to make "ugly" expressions so they double down on making everything anime-y. Generic Anime has a very limited style and you can only go so far before you enter a roadblock. Go Crazy, Go Bananas, PUSH these expressions, SELL ME ON THE FACT SONIC IS GETTING HURT HERE! Hope you take everything I say into account, I don't really expect you to but I think your art would be far more pleasing to you and other people if you thought of these details more.

clean as hell