Thank you for playing my game. The witch Nouna has to dispel the ghosts with a melody (i.e. a collection of notes), and the notes are hidden inside the ghosts. To get a note (i.e. a musical sound), you have to tap each ghost a couple of times. When a note is released, a "clicking sound" is heard.
However, if you release any note other than "F3" first, then all your progress is lost. And to find the monster with the "F3" note, you need to pay attention to the sound they make when you tap on them. The monster with the "F3" note doesn't growl when you click/tap on it.
Finally, when you collect all the notes to the melody, you are advanced to the witch's musical diary, where you can hear the full melody, and even play it manually if you wish to. Then a button will appear at the bottom to the right, where it'll take you the final screen.
I wanted to add a bit of a mystical flare to the game, that's why I added the melody.