>VS Blue
Really adequate theme. You're facing the biggest asshole you've ever known and if he beats you, you've got to start all over again from Lorelei. Really got you pumping as a kid.
>VS Red/Lance
It's that epic showdown on the highest peak in both Johto and Kanto, a battle without any spectators. It fits Red more than it fits Lance, desu. Definitely does not fit Silver's final match at all.
>VS Steven/Wallace
The aggression in the theme tells you "This motherfucker is going to assrape you with the hardest type to face. Wallace was a mistake, and the theme is wrongly used on him.
>VS Cynthia
I don't feel like it conveys the whole "You're facing the baddest bitch in Sinnoh, whose team is designed to be diverse and freaking hard to beat" message. It sounds like more of a rival than a champion theme desu.
>VS Alder
Honestly, it doesn't fit his theme of "Champion who is recovering from a hard loss in life". It fits Benga more.
>VS Iris
This theme just screams "Dragon princess who goes rawr~ :3 before the fight". It reminds me of Rainbow Road, but that only makes it fit the battle stage even better. The most underrated one.
>VS Diantha
I don't want to sound like an edgy contrarian in this thread, but it's as bland as Diantha is. I really don't get all the love for this theme.
>VS "Kukui"
It's not Kukui's theme, but he's the first title challenger you fight, so eh. This one is really well-composed, especially since it draws from the main theme. It finds wonderfully as a "This franchise has been alive for 20 years, we hope you love it".
>VS Hau
And this is where they ruin the amazing theme, by mixing it with Hau's "comic relief" one.