I'm a huge sucker for this trope.It's basically when one of the game's main (typically upbeat) themes has an evil counterpart. For example:
Wind Waker's Great Sea theme:
Dark reprise:
Context: After catching wind of Link's progress, Ganondorf casts a dark spell over the Great Sea, inducing an endless, stormy night in order to make it more difficult for Link to voyage back to his home island. Fittingly, the music that plays during this section of the game is an ominous reprise of the traditional seafaring theme, interspersed with Ganondorf's own theme for effect. It's one of the favorite sections of the game.
Jade Cocoon's hub village theme:
Jade Cocoon is a criminally underrated JRPG for the PS1 that combines elements of Final Fantasy and Pokémon to create a pretty solid game with a great story, top-notch voice acting, an innovative monster merging system, and character designs by Studio Ghibli. And, on top of that, a killer soundtrack. The only problem is that the game is pretty short--but I digress.
The above theme plays when you're visiting your home town, which serves as the game's "hub." It's a gentle, sweet, and welcoming little melody that's quite pleasant to the ear. Perfect for your peaceful, quiet village.
And then we have its dark reprise. I recommend that you avoid listening to this track if I so happened to pique your interest in the game--if you want to check it out, it's better if you go in blind, I think.
Context (spoilers, if anyone cares)
This track plays during a particularly unsettling and feelsy section of the game. Late into the game, an important character is about to be sacrificed to the God of the Forest in order to save your village. This character reveals herself to be Azura, the goddess of sewing souls--or, as she's known by the townsfolk, the "Goddess of Death."
Using her powers, she siphons the souls of all the villagers away, zipping them into the ether. Their physical bodies on Earth are instantly turned to stone, quieting the village completely. You find out about this all on your own; as you walk into each individual house, you discover that everyone has been turned into stone--even your own mother, who sits peacefully in her home, completely oblivious to all the tragic shit that's transpiring.
All the awhile, this lonesome, empty-hearted, and almost bone-chilling reprise of the traditional village theme plays. It's quite beautiful, yet very sad. It makes me feel hollow as fuck every time I listen to it.
Shining Force town theme:
Dark reprise:
Context: This track plays after your home city gets
destroyed by enemy forces, which kickstarts the rest of the game's plot. It's amazing to me how they took such an upbeat, happy-go-lucky tune and arranged it into this heart-wrenching funeral dirge. Walking about the ruins of your city and spotting wounded soldiers all over the place with THIS song playing in the background is quite the affecting experience.
Do you have any favorite examples of this? I can't be the only one who loves it when games do this.