(Press E to skip the "cutscene" at the start.) Oh man, this evil cat is trying to destroy you, AND your computer! Use your cursor to evade attacks from the evil sprite. You only have 1 life, so dodge and move with purpose. That circle is your hitbox, just an FYI.
All by myself. This started as a somewhat passive game, but it slowly just turned into what it is now. Your Best Nightmare- Toby fox, Undertale.