ANIMATION
Kudos for your clean animation style, and also your FBF gusts of wind and dust. Those were quite good. I think you could incorporate more Squash and Stretch in future scenes with your characters, especially since they're fighting, and even more since you're primarily using tweened animation.
WRITING
There were some interesting features in the writing: A tornado, a train, an underground factory. I was left wanting more from the story, though. It would've been nice to have seen a little more setup for the fighting, or at least some narrative that gives us an idea as to the cause of the conflict.
WRITING: S & P
Some 'setup & payoff' wouldn't hurt, either. You see this used in movies a great deal. James Bond films are a great example: In each film, does James simply walk into the villain's hideout and whip out his awesome gadgets / weapons to unleash ultimate destruction--- THE END?
No. There is a almost always a setup. Enter 'Q Branch', who gives James access to specialty gadgets, guns, and usually a car. Having this 'setup' early on allows us as viewers to anticipate their use later on.
In your case ( an animation short ), you don't necessarily need the kind of elaborate setup that a James Bond film does, but let's take a look at a few elements that could benefit from this concept:
Payoff:
Protagonist uses a shot of stimulant to revive himself.
Where/when did he get this stimulant? Did he make it himself?
Setup:
A scene in the beginning of the animation showing the protagonist arming himself with several things. His weapon, costume, stimulants, etc. Having seen the stimulant early on allows us to anticipate its use later on.
Payoff:
After throwing the Antagonist's head through a rock wall, the Protagonist notices that behind the wall is an underground hideout full of weapons and vehicles.
Setup:
While the Protagonist and Antagonist are fighting, we see man-made steam vents and gauges in the rocks around them. This suggests that the environment is not quite what it seems, and allows us to anticipate the appearance of a hidden base later on.
Always try to ask yourself:
Who?
Where?
Why?
When?
How?
What (with)?
MUSIC
The music made for a nominal sonic backdrop, it kept the pace going. It also had very little variation, and got predictable after a few minutes. For your next project, find a soundtrack that has slow parts and fast parts to help you build anticipation along with the story.
SUMMARY
Keep up the hard work on your animation! It definitely shows!
Look at some of your favorite animations and STUDY them. What are the main features of their story? How did they setup their conflicts?
Good luck!