Originally posted Mar 7, 2016

The idea to this AU is that it's mostly the same but the boss monsters are mythical avian-based and the underground run with the theme of feathers and persona mask and the mountain they are trapped under acts like a giant bird cage. Boss monsters are in fact combined with mythical birds that, when in battle, change into avian-based forms. When in these forms, a persona mask bares onto their face with large wings capable of flight sprouting from their backs, they also bare many traits of the mythical bird they are based on like both Sans and Papyrus baring powers of fire due to their mythical avian 'breeds'.

Papyrus is based on a phoenix he calls a 'Sun Flame' breed (bright orange fire) and by default with them being brothers, Sans is believed to also be a type of phoenix (though not proven) Papyrus calls a 'Black Ash Phoenix'(blue fire), though his own powers and battle form has hardly ever been seen. Most believe it's cause he's too lazy or that he may not even be a boss monster at all--since he hasn't shown to be a fighter. But Papyrus believes in him and has seen evidence that he has power of his own in the past.

If you'd like to read more, it'll be posted in the comments!