Nice job with the art and animation, i can see the comics look inspiration, i liked the intro.
You should tell the player how to control the character, also make it so you can move with the awsd keys too.
When you destroy an enemy, you should add particles to see them explode, and a visual effect for when the player is hit, like the sprite flashing red and a sound effect.
The player attack should have a cooldown so you can't spam it (the boss was destroyed pretty fast with this). I played with both characters and their gameplay was the same, maybe add some cool ability unique to each character?
Anyway, good job with the game!