My generic idea was that LBFF would be hopping around and those that saw/interacted with it would suddenly hear the song in their head and at the end of the song, turn into a field mouse.

Could RNG it so LBFF is someone suddenly contagious with it.

Good Fairy is RNG'd - someone suddenly either thinks or gets gremlin bit to believe it, and goes chasing LBFF to turn it into a goon before it can do more damage.

I should not plot ever.