Nice pixel art and animations. I'd love to see this turn into a complete game.
Just two things:
- Z and X aren't the best choice for controls since the two keys are not next to each other on all keyboard layouts. On the German keyboard for example the Z key is at the position of the Y key on the US keyboard.
- I couldn't find a way to quit the game, so I had to kill the process instead. Maybe you could open a menu when hitting ESC that lets you end the game.