This is it. You've fought your way through countless dungeons, past myriad abominations and Evil Overlords, and even across millions of years of time. Your heroics have been accompanied by more awesome pieces of music than you can count. You have finally shown Lavos who's boss--perhaps by crashing your DeLorean into it at approximately 250,000 miles per hour and somehow surviving--only to discover the real Lavos was deep inside, a hideous cycloptic alien monstrosity with appropriately awesome Final Battle music. You bashed its brains in.
Only to discover that was actually just a giant alien mech, and, no, really, the real Lavos, the Lavos Core, was inside that. And just so you know this time it's really real, the Lavos Core sends you spiraling through an insane mishmash of time warps while it makes its last stand, its final attempt to kill you so it can get back to being Devourer of Worlds.
You have to admit, that is really damned epic. And it requires an epic piece of music to accompany such a battle for the fate of time itself.
And it got an epic piece of music.