To me he kinda looks like he's shrugging instead of breathing. Maybe reduce the amount of shoulder movement and add some movement to the chest. That's just what I would do, but then agian I'm not an expert at animation so...

Nice color palette though and a solid character design.

I'm fine with the shoulder movement, but for the tail you should make the movement go forward and loop, like a snake. (Difficult to explain...)

Look at the head. Look at it again. Look at it once more. Why does the body move so much, but the head stays steel solid? Also you need leg, arm and weapon movement.