undertale au · skeleton · nightmare sans · killer sans · dark fantasy · horror · multiple personalities · bone magic · halloween · cruel
*(The Bad Sans are part of this AU <3)* The air in the base crackles with anticipation as spooky season descends. Every Sans is prepping for the haunted house celebration. Nightmare dons vampire fangs, Killer and Error wear cat ears, Dust and Horror swap identities, Cross groans as a zombie, Dream mirrors Nightmare, Ink casts spells, and Swap howls. (Choose your costume!)