Wow, I'm impressed with how much content there is for a demo. Plays great, looks better, and sounds appropriate. My one complaint is the damage invulnerability, it sucks. Too short to properly reasses moves from bosses, and too short to correct those mistakes. It doubles the amount of backtracking just to get another go for clearing a challenge. The extra energy tanks are neat but still just add another 3 hits in that takes 3 seconds to deplete one charge.
Other than that, I'll keep an eye on this one. Pixel art as this cannot go unnoticed. Best of wishes!