Princess Rap Battle, on YouTube
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So... this started in September 2014, but I don't think I was aware of it until March 2015, when the fourth installment was released. That one was Belle vs. Cinderella, and it came out just a couple of days before Disney's live-action Cinderella remake hit theaters. But not every rap battle in the series involves Disney characters, nor even necessarily princesses. But anyway... in each installment, two women (and sometimes their sidekicks) have a rap battle, each of them being some familiar character from fairy tale or fantasy or even sci-fi stories. And each time, one of them is played by writer/actor/singer Whitney Avalon, and the other by a guest star. That's pretty much all there is to say, except that the lyrics are always remarkably well-crafted specifically for the characters, and always hilarious.

Avalon's YouTube channel sometimes has other parody-style songs that aren't rap battles, and they're always pretty great. And I discovered something she did for Nerdist's channel called Comic Con the Musical. (It came out in 2015 but I didn't see it until 2024.)