I vote for Elder Princess Shroob. This theme along with the stormy, cloudy background makes for an epic battle scene. This theme does not even sound like something you would hear in the Mario series. It was more in line with a Final Fantasy song. I loved it. ^_^
Well sometimes organs can be quite heavy but sometimes they can work very well, like here www.youtube.com/watch?v=qtwczv_JACk (seriously this song is probably my favorite from the game...just perfect "bring it on music)
: D Yeah I actually have thought of making a "favorite videogame music" topic where we can post our favorite songs in games : D