An unused interaction with Melody Pianissima in Luigi's Mansion found in the game's files has her play Totaka's Song, the recurring musical Easter egg in games composed by Kazumi Totaka, which is then identified as "Totakeke's theme". Totakeke is the real name of K.K. Slider, the dog musician character from the Animal Crossing series, where this song is his theme, and called "K.K. Song".
Of particular interest is that Melody Pianissima claims to have written the song herself. This raises a number of possibilities:
1. If Mario and Animal Crossing are taken to exist in separate universes, then this song appears to exist diegetically in-universe in both, but have different origin points, being composed by her in the Mario world and by K.K. Slider in the Animal Crossing world.
2. If both of them take place in the same universe, then K.K. Slider didn't actually write his own theme, but rather had it ghostwritten by Melody Pianissima (in both the sense that it was written without credit and that it was written by a ghost).
3. Melody Pianissima could also just be lying.
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