but it likes the normal seance where you about to fight papyrus but his like "BUT HUMAN I SHALL NOT FIGHT YOU, AND INSTEAD I SHALL USE THIS HAS A LEARNING OPPORTUNITY, FOR MY BROTHER SANS" then boom sans who like confused at first but then just doesn't care. and papyrus would be in the background holding a sign that says "go sans, THIS SIGN WAS MADE BY HIS GREAT BROTHER PAPYRUS"

but like at fist the battle is a cake walk just like a small, slow, moving bone but then like sans throws in some pranks for attacks like a whoopee cushion shockwave or a ketchup blast. and papyrus would be helping with every bone attack like adding more bones, changing the color of the bone while its out, or making it taller.

and like the ending attack could have a Gaster blaster covered in shadows but its reviled to be like goofy cardboard cutout then you go thought sans's super boring move that just some tuff parkour with the blue soul.