Dive balls. There are Dive balls in Pokemon Black and White, but no reason to use them because there's no underwater grass. PROOF.There are also quite a bit of 3rd gen pokemon being made available in BW2, and they even made the gym structure somewhat similar. I hope RSE remakes arent next for 5th gen, but it seems highly likely that they are.
the Hoenn battle theme is in the game files. I'm assuming its for the world tournament with the rest of the newly made themes