After a experimental gone wrong sans and papyrus turn into a skeleton gaster blaster dragons frisk takes care of them she or he is 19 everyone is at the surface but they cant see papyrus and sans make your character and find climb to mt ebbot and save sans and papyrus and free them turn them back to skeletons again feel free to interact btw SAVE THEM and again make character save sans and papyrus and make an antidote to turn them back to normal and frisk chara and asriel will help on your journy