As for the song you partially remixed, I had no idea, till you said what on the video description...

As for this piece itself, it sounds good! I haven't read Past Sins, but I imagine it fits quite well...
I always thought of big, climactic battle themes to be much more fuller though (you said you based it on the final battle?). It is full for the most part, but there's some parts where the role of 'filling' the harmony is given to the percussion, which doesn't do a godd job of it...
I know there are other instruments playing, but the percussion seems to be dominant when filling what the melody isn't doing.
But that's only for some parts, other parts really work!
Great Job!!!
TubeyouYou are the hero My Little Remix deserves, not the one it needs.
So we’ll hunt you. Because you can take it. Because you’re not our hero.
You’re a silent guardian of music, a watchful protector of songs.
A doctor of dissonance.
-Phillypu