Villain Song/Literature

And so he spoke, and so he spoke,
That lord of Castamere.
But now the rains weep o'er his hall,

And not a soul to hear.

—The Rains of Castamere, A Song of Ice and Fire

The Goblins' songs in The Hobbit.
Shows up a lot in Redwall. Triss has three ("That's The Freebootin' Way", "'Tis Nice To Be A Villain" and "Plunder, By Thunder").
- In Rakkety Tam, the villains sing a let's-get-frenzied song, which the audio book sets to a heavy beat and bass guitar.
  - Also in Marlfox. "Who be death? We be death! Dis de blade wot stop your breath!"
- And then there's Flinky's many songs in Loamhedge. All of them are great, but the darkest is the "Vermin Lullaby", which was a normal lullaby at first, before it suddenly got Darker and Edgier in the second chorus.

"So hush now, lullaby, foxy close yer eyes, and you'll soon make lovely vittles, for the ants and flies". Squick.

The Star Trek novel "How Much For Just the Planet?", being a rather... different... Trek story, features "My Own Sweet Tyrannical Way", sung by Queen Janeka. Having captured Sulu, McCoy, and a pair of Klingons, she launches into a high-kicking musical number about what a pain in the ass is it to be a barbarian queen in these crazy modern times... her litany of complaints include an uncomfortable Chainmail Bikini, dodging Klingon Promotion attempts, keeping a rowdy barbarian horde under control, and paying the heating bill for the Underground Lair. Though in the end, she concludes it's totally Worth It, since the Evulz are too much fun to give up.
The closest thing to one in the Left Behind books is Nicolae Carpathia's self-indulgent national anthem "Hail Carpathia", which gets twisted by Buck Williams into "The Villain Sucks" Song "Fail Carpathia".
A Song of Ice and Fire has "The Rains of Castamere" which recounts how Tywin Lannister deals with uppity bannermen.