Music glitch at the Pokemon black league?

Question

I was battling alder when some weird music popped up instead of his theme music. It sounded a lot like Diantha battle music. Is this normal or is it glitched?

Answer 1

This is not a glitch. In Generation 5 games only, there is a feature that will change the battle soundtrack when you are fighting against an important trainer, such as a Gym Leader or in your case Alder, and you have them down to their last Pokemon. You can listen to it here; it does sound somewhat like Diantha's theme.

This feature has never returned since Gen 5 (unfortunately) so it likely feels foreign seven years later!