When the party is comprised of Yoku and Jack, such as in the Spoilerlands, this song will play. There will be different battle themes for different parties, such as Spoiler, Spoilery, and Spoiler McGee. These, however, are just for random-encounter enemies, not for big bosses and recurring opponents like Sir Spoiler and Spoilertron.
Just wanted to give a little sneak peek. Other sneak peeks will come out soon, including the big battle against King Spoiler of Spoileria! (those are all joke names lmao)