eishya and DexRunner This is the very raw rappresentation, and yes the dark thing is meant to be the sword's smear. And I will move this in the WIP section, but thanks for responding me in first place and helping me. I've been struggling for hours just to figure out how it works!

Is the dark smear meant to be the sword's smear, or some sort of magic? Being so dark compared to the sword, it doesn't really feel like it's a smear of it.

I also feel it slows the swing down rather than making it feel fast and smooth, because the smear lags behind so much and takes so long to complete. Smears aren't a magic bullet, they can hurt an animation too.

What is swinging the sword? It seems very strange for a sword to just... turn 90 degrees like that. What sort of attack is this? I recommend animating it together with a character, even if it's just a roughly-drawn placeholder character.

Nice!  Makes me think of the fencing level in Robin Hood Prince of Thieves for NES.  It's hard to say what to improve without knowing the intention of your final results.  Are you wanting it to be more realistic or more outlandish or do you want it to be simple or cartoony?  What problem do you think it has?  It might be better to move it to the forums if it's just a WIP.  Admittedly, if it's not at a point of being close to finished or it's a small part in a whole animation/sprite, most patrons voting in the public queue aren't likely to approve it for the gallery.