"Who Is This "Moon"?" is an instrumental score for Sing.
It can be heard as the bears confront Mike about the money he cheated them out of in a card game.
Mike tells the bears that Buster Moon has the amount of money they are looking for, but it is then revealed that Buster lied about having the money, much to the shock of the contestants and the fury of the bears.
A large crack then forms in the glass floor and wall, and the music ends right before all the glass shatters and floods the Moon Theater.
Lyrics
(Instrumental)
Trivia
The score's title refers to a quote from the bear leader, when he asks who Buster is.