Nice work-in-progress. The actual running animation looks nice and smooth, just like how it's supposed to be animated. However, the backgrounds don't look natural and look too mechanical and sloppy to properly complement the nice running robot you have there.
The line tool was never something I was personally a fan of, though in some cases, it can look nice. I would suggest, when using the line tool, changing the thickness of the lines so it has more variety and doesn't look as mechanical.
Sometimes it looked like you put dabs of other unfitting colors there to make it look more detail when unfortunately, all it does is completely mess everything up and make it look absolutely ugly. You'd be better off with gradients, shading, or actually, y'know, adding more to the background to make it look more detailed.
Would've been a lot better if it was longer
Also, is it me or does robot move without motion tween when he is running up stairs?
No sound also
And most important too short
Nice prelude to something full on.
And, admittedly, this is just that. A test for a more fleshed-out feature.
.....kinda reminds me of Mega Man.....
In any case, despite being a short loop with no audio, it looks promising.