Basic idea: The party will be a band who came across magical weapons that turn into instruments. They don't start off strong, but I plan on having the instruments get more powerful with the player's popularity. No bonuses at first, but can get +1-3 over time, and the players can choose some magical effects as time goes on. The idea is they will perform in a Band Battle against some of the bosses, granting them a Favor of the Rock Gods die. Think Inspiration dice, but it can be stacked (You aren't limited to one at a time, and can be used more than once if you have it), can be granted from one player to another, and can be used to grant advantage or used as a free re-roll. They won't be more frequently given than Inspiration dice, just a special bonus to be gained whenever they vanquish a band in a music duel. (May also have performer duels, like the guitar duel from Six-String Samurai)
Already came up with some enemies and their Battle Songs, but I'm looking to see if anyone else has any ideas. For instance, one of the bosses is a Lich with skeletal arms grafted to his body that allow him to play a double-necked guitar while his still fleshy arms handle a microphone. His battle song is Necromancin Dancin by Bear Ghost, with a three-headed flesh golem providing backup vocals and Keys/Synth, a skeletal champion with bass strings along his spine as the bassist, and a ghoul with human skin drums.
An order of Holy Paladins (Not intended as bosses, but who knows where the party will go?) will play In the Name of God by Powerwolf, a demon cult will play We Sold Our Souls to Metal by Soulfly, and their first battle will be with Tou to Rial the Performer (Illusion/Evocation hybrid wizard) who will play Wizard Lovin' by Neptune Power Federation to show them how the band mechanic will work.
Basically, I'm looking to include more factions that could be included, and what their song should be. I want a Drow faction with an emo-ish sound (was thinking Miss Murder from AFI), and maybe Shoog Shoog by Hu Band for the Dwarves (Initially thought Hu Band would fit with Orcs, but the English lyrics actually read more like a Dwarven song). Don't have to come up with a Battle song for each faction/race, but I'd be up to have a playlist just in case someone decides they want to challenge halflings to a rock off.