If You Take Another Step Foward...

First of all, this caught my eye from the group stack. That's something. This piece is very fluid and has a lot of motion to it. It has the 3-D effect that your going for.
Let's start with the bad stuff. I don't like the feet/slippers thing at all. He's a skeleton, but it looks like here he just has white skin. It threw me off a little. Second, the bones in the front don't quite pop out at me as 3-D. I wish they overlapped in front of Sans a bit more, or had a more noticeable shadow. The third (and probably final) thing I don't like about this piece is the weird, foggy magic effect you did in front. It doesn't mesh well with his coat, and it draws your attention away from the important things- such as Sans's face and the soul. I think you could remove that, and this piece would be just as powerful.
Last thing! In the text box, you used the wrong "you're". Make sure to spell check!

I love this piece, I really do. But like all things, it can be improved. I hope this critique helps you!