If you want strong effect you should remove some of the frames, cause it slows everything down and remove impact.

Here's the suggestion:

Scuba diving in nes palette. It could use more work but I can't spend anymore time on this.

@wolfenoctis Thanks. I've decided to try these daily challenges but not sure how long I will have spare time. It's interesting so far.

Another one. Theme was "peace".

Now you've made second step slower which also slowed down the action. It's all up to you and what you aim to get but I think that to suggest force, actions needs to be strong and short, recovery from action can and usually should be slower but action itself not. But don't get me wrong more frames make everything smooth and appealing so you need to find balance between number of frames and how fast actions should appear.

I think that you have two unnecessary frames at the beginning of first swing which make animation slower and take away the force of the swing.

Simple edit: