Ender Dragon Boss Music Pack
This pack should work on most Minecraft Versions. It definitely works on 1.12-1.18 and it may work on even earlier versions, though no guarantee for that.
This is a very small resource pack that adds some nifty boss music to the Ender Dragon Boss Fight. The pack was originally made for a planned Pixelmon Modpack, however this idea was sadly scrapped so it is released as a standalone pack instead.
The used soundtrack comes from the games Pokémon Sword and Shield and is the theme for Max Raid Battles against Legendary Pokémon. However, it really doesn't sound like something from the Pokémon franchise specifically and it really works well with the Ender Dragon... why don't you give it a try?
This is the ideal pack for you and your friends if you want to make your Minecraft experienced that tiny bit more epic and enjoyable. You can use it for free wherever you want without having to ask me.
Use it on your modpacks, on your servers... just don't act like you made it, okay? ;)
Have a great day!