In the menu, use the left arrow key to highlight fight (gives you a chance to attack), right arrow key to highlight spare (skips to avoiding projectiles), down arrow key to highlight item (use a helping item), and up arrow key to highlight weapon (currently does nothing). Press Z to confirm an option. In the battlebox, use the arrow keys to move around and avoid the projectiles. Touch the yellow projectiles to attack Cactufine.
The idea for this came from Undertale, which is obvious, and so does the music. Undertale and its music was created by Toby Fox. This project is a work-in-progress, so let me know if you notice any mistakes or glitches!