('Metal Crusher', as heard in Metal Crusher)
'Metal Crusher', alongside 'It's Showtime!', 'Hotel', and 'Oh!', serve as Mettaton's leitmotifs, appearing in various contexts relating to the character.
(Mind you, it's highly recommended to read these articles together!)
'Metal Crusher' serves as Mettaton's battle motif, appearing in both Metal Crusher and Death By Glamour (with an additional appearance in Last Episode! ).
As discussed on the page 'On the Origins of Undertale and Deltarune's Leitmotifs', the 'Metal Crusher' leitmotif originates from Noisemaster, a Cucumber Quest fan-song.
Finally, Metal Crusher 's beginning jingle (which in and of itself sounds very similar to the 'Metal Crusher' motif) is heard on its own elsewhere in the soundtrack, and will be covered here:
('Metal Crusher (Intro)', as heard in Metal Crusher)