Allow me to fill in the rest of the cast:

Asgore as Brad Majors (Asshole)

Toriel as Janet Weiss (Slut)

W.D. Gaster as Dr. Everett V. Scott

Papyrus as Rocky Horror

Sans as Eddie

Gerson as the Criminologist



Also, (and this is just my opinion) I could see Muffet as Magenta a bit more. Just sayin'.