Perhaps not a boss theme...
I sat here for the first couple of minutes waiting for a rain effect, rain stick, or some other sort of sound that would mimic rainfall to come in. I was very pleased when you delivered on that front. The thunderclaps punctuate the piece just right.
The opening drum rhythm is another of my favorite rhythms (hi-hats moving in an eighth-two-sixteenths pattern of open-closed-closed, combined with any backbeat). I was sad to hear that it was used sparsely throughout, but it was for the best: rhythmically, this piece is sound.
The faux-guitar work is spot-on, and I found the addition of a piano to the mix to work quite well.
Because the common assumption of music on the Audio Portal is that it may more likely end up in a Flash game on the Flash Portal than in a movie, I think this theme works better as the BGM for an entire short, perhaps focused on one battle, in the rain (natch).
And of course, I happen to pick my AP review omnibus night to be the same night where I should be writing an essay. At least I have good tunes to write along to, as well as music that's not putting me to sleep. Good job again, Shawn.
~Joshy676