Batshit

This isn't too bad. Heart sprite is fucked up though

I like the concept, but you can add more various obstacles so it would be more interesting to play

So I think everyone else has already said these but, I like the concept. I liked the bullethell-light mechanics from undertale but the up-down movement scrolls the page and the attacks here are extremely simple and repeditive. Keep working on this concept with those two things in mind to improve upon.

also you should make it more clear and impactful when the player gets hit. Add some blinking/invincibility frames, and a hit sound. Also I'd say use original music. Taking the gameplay concepts is fine but the music is just straight up stealing.

Its not very good moving up and down scrolls the page its annoying.