so this au is underfell mixed with storyshift and underswap as the name suggests.
roles:
chara is in papyrus's role. however the genocide run is set in disbelief unless it states clearly its disbelief, in which case metta would double-battle frisk and asriel. her cannon lover is papyrus, but if he died maybe metta could get his hands on her heart
frisk: frisk is in mk's place but lives with the dreemurs as her mother,father and sister died a year before the events of the au. she has three cannon(ish) lovers...asriel,sans and metta.
asriel: in sans's role, asriel is the mischievous son of and asgore. asriel loves his sister chara and frisk. he sometimes steals frisk's stuff like her sticks (don't ask shes crazy) asriel doesn't like metta and frisk being together, or frisk and sans...he's a yandere in the making
papyrus: he's in asgores original role. papyrus was rendered blind when someone (g $+èr) tied a magic blindfold around his eye sockets, he can't take it off nor can his protecter (chara) because it hurts him too much. his brother was announced dead aboud ten years before the main storyline took place.
sans: in toriels original role: he was locked in the ruins and announced dead, he tries to keep sane all alone, in the ruins but his sanity is wearing thin. he's about 18-20 years old just a little older than frisk. he feels an attachment to frisk, and thinks of her as innocent,naive and kind in general.
toriel: in alphys's place. toriel is the royal scientist who studies mental health and vaccinations, but since she hasnt been properly trained in the medical field as human docters have, the vaccinations almost always kill the one who receives them, she is married to asgore but their marriage is on the rocks.
metta: metta is in frisks place and is the protagonist of ssfd! he fell down after being bullied for having mechanical body parts. he soon meets a talking monster plush and takes it everywere with him...
monster plush/kid: monster kid is the adopted son (along with napsta) of toriel and asgore before chara,asriel and frisk. he went along with napsta's plan but soon died along with him. monster plush is ssfd's flowey.
napsta: in chara's original role...i haven't thought of any thing for napsta yet or for any other characters yet. the farthest in development of ssfd i'm in is papyrus sans and g $+érs conflict.
routes.
ssfd has a little bit more routes than undertale. these routes are listed with the final boss
pacifist- monster plush
true pacifist- napsta blooky
neutral- omega monster
genocide-chara
true genocide-[double battle] chara and papyrus
dark genocide-yandere asriel (fight for frisks love (uwu)
disbelief-[double battle] frisk and asriel
so thats all the development i have for ssfd i'll update once an update comes to the au.
i think the next thing i'll be working on for it will be character outfits...i have to improve asgore and toriels clothes a bit along with alphys and undyne