Hi there..
I think the scale-up and re-detailing is fine, the color themes you have chosen could be better, in particular on the wolf guy.. his eyes and hands seem completely lost , and your last 2 "evil (i assume)" variants, the eyes on both need a little bit more work.
But to be honest I question why you are doing this, if its a case that you are experimenting with pixel art then why not try develop a character out of your own imagination? It can be inspired by sonic or something else, but I think the problem with copying something so closely as in pixel by pixel, is you are not going to get experience with being creative yourself. My suggestion is try, try, and try again to make your own works and after seek reference from other peoples work to see how you can improve it, rather then take someone else art first and trying to improve / mod it.
I hope to see something out of your imagination next time
Keep at it