I love it, it's really fun! I don't understand at all how making the lines and the equations work, but even with that, I had fun.
Like, I made a line and I thought the number next to the plus or minus made the equation, but it took other numbers instead.
I couldn't tell when it was a shield or when it was damage.
I didn't pay attention to the deck, I didn't notice that is there until I read what feedback you were looking for.
I mostly just cleared lines, tried not to lose, and beat a few bosses.
The art is amazing! Maybe adding a background or even a simple parallax could make it even better. As for the rest, I love the slime, the bosses, and the UI.
This is a really good game!