Boss battles - at least the final boss - often have their own battle music and maybe background.
In RPG Maker MV there is only the option to set one battle music in the database, which you can change later on
using events. But you have to change it back after the battle event or subsequent battles will use the same music.
The same goes for the battle background.
I myself forgot to change it back multiple times and the result of this was this plugin.
You can set troop specific battle music and background that will only be active during the battle against this troop via comments on the first page of the battle events:

Their are 3 different comments:
BattleBgm Name Pan Pitch Volume, where:
- Name is the name of the sound file
- Pan is a number between -100 and 100
- Pitch is a number between 50 and 150
- Volume is a number between 0 and 100
BattleBack1 Name, where:
Name is the name of the image file in your projects img\battlebacks1 folder
BattleBack2 Name, where:
Name is the name of the image file in your projects img\battlebacks2 folder
Troops which do not have set up any of these options will still use the default options.
The options are even active for Battle Test, so you can directly check if it works using the editor.
Plugin usage and credits:
Plugin is free to be used with commercial and non-commercial projects and does not require any credits, yet they are still appreciated.
You may repost this plugin.