JCoxeye's Leitmotif Index:


('Oh!', sections A and B, as heard in Oh! One True Love)

'Oh!', alongside 'It's Showtime!', 'Metal Crusher', and 'Hotel', serve as Mettaton's leitmotifs, appearing in various contexts relating to the character.
(Mind you, it's highly recommended to read these articles together!)

'Oh!' serves as an extraneous melody pertaining to his opera, Mettaton: The Musical, and is later reprised in For the Fans.