Sans- Green Day, listens to WAKE ME UP INSIDE of course

Papyrus- Katy Perry, also listens to Drop Pop Candy

Frisk- Skillet, they a hardcore cinnamon roll

Alphys- Anime soundtracks

Undyne- Taylor Swift, just won't admit it. Also anime soundtracks.

Asgore- older bands like Nirvana, or the Revivalists

Toriel- Maroon 5

Flowey- listens to Meghan Trainor when nobody's watching