I went with arguably the greatest episode of The Real Ghostbusters animated television show, "Ragnarok and Roll."
|Jilted boyfriend turned supervillain Jeremy.|
The rest of the plot tracked with the episode: the heroes fight some flunky monsters, notice a pattern to their location, meet the girlfriend Jenny, and head off to stop Jeremy from plunging the Earth into frozen chaos. Rather than just dogpile onto Jeremy, the Lioness manages with some jammy dice rolling to disarm Jeremy, knocking the flute free, and then talking him down from his plans to destroy the world.
The big bad guy reveal at the end wasn't some bodiless head, however, but rather a mysterious sorceress named Rune, who leads a group of ninja ghost warriors called the Phantom Beasts, who just happens to be the group the Lioness is tasked with fighting. BIG emotional payoff for my daughter and the rest of the group for realizing that, for the first time in the campaign, they have saved the world.
|"Sorceress Ryth" by liiga, a fair representation of Rune|