By hijacking the function the game uses to play the music sequences for Ocarina songs, you can have the game play different music depending on what the boss is doing. Here I demonstrate some Twilight Princess-style "boss is vulnerable" music, but it could be associated with any boss action.

This is labeled a mod concept because I haven't actually made the mod. It's only 3 instructions to start/stop a clip, but it would still require a bunch of disassembly of boss ASM which I don't feel like doing. For this video I just edited the RAM on the fly to make the music play. The Ganondorf part is a little glitchy due to some odd behavior with his BGM that would need to be fixed in a real implementation