The animation looks serviceable to me. The animation is very clear (although adding arms might complicate things) and doesn't look too stiff. I see two points that would improve the animation:
First, the posing is awkward. The way the head and body is placed it looks like Mario either has a straight back or is leaning backwards, which looks odd. He should look like he's leaning forward (unless you're deliberately going for a weird pose, but that would be more suitable to someone like Waluigi).
Second, you could improve it by adding some secondary actions, i.e. things that would move as a consequence of the up and down motion. the hat could bob up and down by a pixel, and you can distort the shape of the body (like a ball's stretch and squash) or make his gut bounce.
First, the posing is awkward. The way the head and body is placed it looks like Mario either has a straight back or is leaning backwards, which looks odd. He should look like he's leaning forward (unless you're deliberately going for a weird pose, but that would be more suitable to someone like Waluigi).
Second, you could improve it by adding some secondary actions, i.e. things that would move as a consequence of the up and down motion. the hat could bob up and down by a pixel, and you can distort the shape of the body (like a ball's stretch and squash) or make his gut bounce.