@picopepin I may have made this remix, but this was your doing. XD
(Some credit where credit is due: The MIDI file I used as a base was made by "The Music Decomposer", you can find their MIDI file here. )
I had some odd struggles getting MTT to sing this song. Turns out the vocal range of the song is difficult for him. (ಠ‿ಠ)
For context: Mettaton's dialogue voice has nine sound beeps. But some of the beeps sound better in the "Tenor" range, and others sound better in the "Baritone" range. None of the beeps cover both ranges at once. So normally I just pick which beeps are appropriate for that vocal range.
But the key of this song forces MTT to sing at both ranges, some parts with a near octave jump.
Which meant that if I picked a tenor beep, all the high notes sound more like Alphys but if I picked a baritone beep all the low notes start sounding like a grinding box fan. And while I could "switch" instruments, that's just annoying to do.
The only way I could make his voice sound reasonably cohesive was to layer one "tenor" beep and one "baritone" beep, such that the high notes don't sound too high-pitched and the low notes don't sound grinding (kinda like hackneyed bass-boosting and treble-boosting where needed). Not that it was difficult, but it took some trial and error with some 20 possible permutations to find a combination I was happy with.