During the final boss battle, at the start of your turn, if your HP is over 75% and boss' HP is below 25%, your theme starts playing.
Has an option to enable music change against any bosses. Can be enabled in: C:\Program Files (x86)\Steam\steamapps\common\LBoL\BepInEx\config\intoxicatedkid.yourthemewhenwinning.cfg
Inspired by musics that play when protagonist is near victorious from animations and games.
Installation: Place YourThemewhenWinning.dll to Steam\steamapps\common\LBoL\BepInEx\plugins