(I don't know if this'd be possible or not, but)

Maybe you could add music from the (pokemon) games into battles. Different ost for each type of opponent, e.g. Mew guy could have "blah blah" ost, while zapmocluno has "yada yada" ost.

Again I don't know if this'd be possible, it could create lag or maybe there'd be legal problems with nintendo or something. If it is possible it'd make battling that much more fun/bearable (then again some might find having music constantly looping, well, annoying.) (Oh yeah, if this is possible maybe give it a toggle) (As with every one of my suggestions, I apologise if my explanation was unclear) >.>

I think it was unincluded due to lag. But, easy way is to find the battle music on YouTube and play it in the background while you're battling. Plus, if you get bored of one, you can always go back and switch between songs. That's something not guaranteed by doing battle music this way.

And people have different tastes about genres so they might become furious if they are already losing and the ost is something like rock but they really are Beethoven's fans.

You'd also have to keep in mind any possible copyright issues that may bring up. Unless the music was specifically created and only used for creed adding music could lead to lawsuits and such which could have the unintended consequence of closing the whole site down. Not to mention every time you pick an attack doesn't the page completely refresh? I won't pretend to be an expert on web-design, but doesn't any added music start over upon the refreshing of a page? That could get incredibly annoying very quickly, you'd hear about the first 3-5 seconds of a song before it started over because you clicked an attack.

i like XD