I believe the track is listed as "Shaman in the Dark", but I could be wrong - the game was released in Japanese so...
The midi for this track can be found here:
http://www.vgmusic.com/music/console/nintendo/gba/index-classic.html
I recently heard this track and it blew me away - it's a classical-style organ piece that just screams awesome boss...
Had I the resources, talent, and recognition in this community I would definitely create a remix myself, but alas, I have none of these traits.
The track sounds like it would translate easily into rock or metal (although simply remastering the song by itself would prove satisfying, but I know that there isn't a single remixer out there who's simply content with exactly what he's been given), and you could also mix it with the track "Maiden of the Dark"(also found on the previous site listed) which is quite literally a slower, music box-style rendition of the exact same song.
On a separate note, the music of the Fire Emblem games intrigue me to no end, and it pains me to only find one remix in the whole archive of OCR. Those not familiar to the music can find it easily- just search for FE music on Youtube...
I understand that this community is not a hired band that plays whatever its customers desire, but I would greatly appreciate it to see these games being covered. Thank you so much for your time.