Press Space and the Health will go down, slowly, the color will change along with it. Enter increases health and changes the color as well. Tweak it to fit your projects and your tastes (with credit of course). You can also use this (also mine, but alt. account): https://scratch.mit.edu/projects/504736623/ which uses more pen than this.
Just felt like doing it. I made an unsuccessful one on my main account, but I had a vision on how to solve it and it works now.