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Frostfell (Undertale AU)

After the war against humans and monsters, during the sealing of monsters into mt ebott, a wide swept snowstorm has arrived, causing the human mages to frantically seal the barrier, but due to the spell being "Weak", this results in snow entering into the hole of mt. ebott..

Soon a witch named baba yaga enters into the hole of mt ebott and as she laughs, the humans realized it's too late, soon the sealing is fully complete and without powerful hunters to kill the witch, they fail to contain the monsters completely and result in the witch becoming the "Elusive" being to the monsters unknown presence

many years have passed.

It's the year 20XX, a legend has been foretold about a witch who lives in a house, a house that is walking in chicken legs, children who went to mt ebott never returned, or some say?
A young child run up to the mountain in hopes of finding a clear answer to why is there a witch.
And upon falling and after being tripped by a branch, they fell down and land onto a bed of flowers. which sprouts blueberries growing.. above is the hole where the winter snow slowly lands. 
Blueberry flowers - A fictional plant that grows in cold regions of europe, found in mt ebott, these plants are cultivated and used in food
Frostdraws - Also know as The witches power, frostdraws is a theory made by Dr. Alphys in a attempt to find a alternative source of magic to use, though while baba yaga hair is used on this, it's temporary on some monsters, but long term use of these powers may fluctuate and result in a frostdraw becoming permanent to a monster. 
There are four routes
Frosted Snow Route (Which involves killing asgore and defeating flowey)
Snowgrave Route (A Genocide route where frisk kills all monsters, defeat sans and flowey, and sparing asgore)
Peace Route (Involving sparing monsters and helping their problems)
True Ending Route (Unlocked by other ending's, Frisk is able to damage baba yaga and defeats the witch once and for all)

Main characters:

Frisk (Frostfell): They're likely human but their skin looks pale by color, has dark-hazel brown hair and a child of sorts, wears a sweater with stripes of blue and white, brown shorts and black shoes. They also wear a assorted colored scarf.
Chara (Frostfell): Somehow a lingering spirit that constantly takes over frisk during snowgrave, Peace and  frost snow, but disappears in true ending route

Flowey/Asriel (Frostfell): Resembling a blueberry flower with a face, Flowey seems to be kind though due to not absorbing the frostdraws, Flowey personality remains similar to his UF!Counterpart, albeit shy and confused about why?

Toriel (Frostfell): The caretaker of the Frost Peaks, a ruin like city which has a expansive tunneling and housed many different monsters, due to her use of frostdraws, she becomes kinder and much more similar to UT!Toriel but will be angry if any of her children act naughty or break the rules. 

Napstablook (Frostfell): Somehow he remains passive and personality overwritten that he no longer has a bad acting attitude and being angry (UF!Napstablook) and opt instead for a lazy, calm and kind self (UT!Napstablook), helps frisk

Papyrus and Sans (Frostfell): The Skeleton brothers duos, both are the guardians of the Town of Solitude, which is Snowdin but becomes a fortress of sorts, according to Sans, Back then, the town snowdin was weak and was being invaded by rogue monsters so with the help of the royal guards, the town became a Fortress and monsters living there are at peace now.
Individual Character
Papyrus (Frostfell): The tallest of the Skeleton brothers duo. Due to the usage of the frostdraws, papyrus gains a ectoplasmic body and becomes muscular long enough for him to feel a bit great. that is his personality seems switching from time to time, whether be his angry and loud-mouth (UF!Papyrus) or calm and Stoned (SF!Papyrus), in rare ocassions, being bombastic and joyful (UT!Papyrus)
Sans (Frostfell): The shortest of the skeleton brothers duo, He maybe the laziest but he can be quite serious in combat, however his jokes are dry as a sand of sahara desert, he uses frostdraws very little and result in his personality remaining the same but gains a ectoplasmic body of a chubby bear. well at least he doesn't feel conscious on his weight.
Undyne (Frostfell) : Somehow the armor remains and stands as a treacherous pursuer, releasing smoke on it's royal guard armor, it chases anyone down with a zeal of rage and bravery, defeating it reveals that undyne was out of the armor the entire time, she uses frostdraws and that results in her personality changing to her Undertale counterpart. the armor undyne used to wear is a guardian of the frozen waterfalls, which is the waterfalls but frozen in Ice
Alphys and Mettaton: The Doctor herself and the Idol. As a progenitor or the one who hypothesized the frostdraws, alphys personality is a mad scientist and is willing to test on frisk and flowey, however after sparing her in a lab experiment fight, alphys reveals her true personality as a kind but shy individual, much like her UT!Counterpart was. Meanwhile Mettaton personality is overwritten by a strange bug called "Spamton.Exe", which is revealed to be the darkner merchant himself, spamton G. Spamton taking over mettaton, after being bested in a Live Idol show, spamton bug is erased and mettaton true personality returns, Also the EX body blueprint is found and reveals that it has strings on it, maybe spamton plan was to "Break" free from the deltarune timeline and join the interesting one. both of them are guardians of the Eternal Core and ColdLands, which is hotlands but have been exhaust of heat and only remains at low temperatures and the eternal core lies in the bound
Muffet (Frostfell): Still remain the same except kinder
asgore (Frostfell): The King of the Royal ground, due to him absorbing all other frostdraws, he is really big and sit down in a throne made out of ice, he carries a "Two handed club like weapon" he called "Rime Shank" which is a powerful tool made out of the baba yaga house who walks in chicken legs, due to the weapon, Rime shank release a faint scent of blueberries.
Asgore personality seems to be switched, in battle, he is angry, furious, and in rage, much like his UF!Counterpart but after defeating him, he returns back to his kinder and compassionate self, like his UT!Counterpart, depending on the routes, he is either killed or spared, which shows his emotion as shock *Frosted snow*, disbelief *in Snowgrave*, relieved *Peace*, and finally, joy *True ending*.
it's revealed that his appearance is very similar to UT!asgore but with rugged scars and eye color being blueberry blue and his outfit being more similar to UF!Asgore, however despite that, his cape looks different, icy spikes formed behind it and reveals to be a comb of a chicken. Upon phase 2 which he uses a dangerous form of frostdraws, he grows bigger till hypermuscular bodybuild is achieved, breaking away his outfit to only a speedo, his eyes turns black and sclera remains the same color. He resides in the castle of the Snow King, which is somehow a frozen-constructed castle
Baba Yaga: The True antagonist of the Frostfell AU, a elusive witch who rides a pot that can fly and with a help of her "Magic" Broom, she flew everywhere, of course her appearance is a hag and looks old, wears hermit clothes and has charms in her neck. She resides at the entrance of the barrier guarded by her house