...THAT song?

Play me a song you’re the Piano Man-

Megalovania?

. . .
Heh, no but your on the right track. PTSD. Pokémon Traumatic Sinnoh Disorder. He's a Garchomp. There are a lot of battles in the Sinnoh games now including Brilliant Diamond and Shining Pearl but most of all Legends: Arceus.
The music he's playing is the intro to one of those battles. But the actual battle them itself in Legends: Arceus. This is the music that has mentally scarred multiple generations with it's menacing implications. And then when we heard it again in a random beach house in Unova, which was my first instance of feeling the sheer panic of dread, I immediately exited back out the door, ran to the Pokémon center next door, saved, then grabbed my Pokémon from the PC with fly and flew immediately back to Nuvema Town and only saved again once I was in my room.

I'm not kidding. I had seen a few episodes of the Sinnoh Anime although I started with Black and Black 2 but as soon as I heard that piano, I knew I had ever reason to be scared out of my mind because this was the song of doom.

This is very much Toby Fox Secret boss levels of fear and anxiety right up there with Megalomania and Black Knife.

I f(Zoroark cry)ing knew it.
Looks like somewhere a team of 6 boys are getting bodied and wrecked.