Old School Runescape has a lot of great music, but the boss tracks from 'Tombs of Amascut', the game's third raid, are IMO peak:
Zebak, a crocodile cursed with an endless hunger, who limits your movement by spewing acid on the ground.
Kephri, a scarab mindlessly spawning endless children, forcing you to cull their numbers or be overwhelmed by an army of adds.
Akkha, a giant warrior whose shadow contains his soul, preventing you from damaging him unless you can clear the shadows quickly.
Ba-Ba, an undead baboon pelting you with falling rocks, keeping you on your toes so you can divert their damage to the scenery.
The Wardens of Tumeken and Elidinis, mechanical guardians of the tomb of Pharaoh Osmumten, who'll test every skill you have to the limit.