The three white Jigglypuffs represents the Chorus Kids, a trio of singing round-headed individuals with a white color scheme.
The Jigglypuff's different sizes and favored Sing references how the Chorus Kids sing in a steadily increasing pitch.
The stage represents the featureless white plain setting of "Glee Club", a singing-themed minigame in the Rhythm Heaven series.
The music track references how "Monkey Watch" and "Glee Club" are both Rhtyhm Heaven minigames who feature multiple characters that look the same, such as the Small Monkeys and the Chorus Kids respectively.
Other trivia:
This spirit's Jump ↓ ability references how the Chorus Kids never jump in "Glee Club".
