I suppose this is also a Gen 9 related story, but when I started playing The Indigo Disc, I had no idea that the battle theme would be a remix of the original Gen 5 battle theme, even though it was gradually becoming clear that the whole area was related to Unova. While I wasn't necesarily too pleased with Gen 9 and the whole DLC situation, this did put a smile on my face and brought back some memories. And I was also excited to learn that my prediction was true, and that fighting a wild Tera pokemon would cause a remix of the special wild encounter theme to play. It was fun being right.
On another note, I also remember watching that awesome animated trailer for BW2 at least a few times a day leading up to release. It was cool for younger me to see pokemon actually fighting, making contact, not saying their names every few seconds and actually making animal noises. It was faster paced, because it was a trailer of course, but nevertheless I thought it was awesome.