Hello ! I have this old fanfiction in 13 parts that I wanted to share to you. That's a Underfell and Horrortale crossover where Underfell Sans and Horrortale Sans switch places for some reason. The updates will come quickly, I just have to translate the story, since it's originally a french fanfiction ! It's mostly a humoristic story, but there are some soft gorey parts. Well, it's Horrortale, you know, it's not really a happy universe.

Disclaimer : The world and the characters belong to their original creators. I don't earn money on my writing.

THE DOPPELGANGER

Part 1 : Underfell

— Ya' sure ya find it like that ? Damn ! That's not a small hole. Ya' know, I'm not sure even Alphys can fix this. That's sure ugly.

— Undyne, could you stop rhapsodize and help me carry him ? He's heavy !

Sans half-opened his eyes. His skull hurt him like someone crushes a bottle on it. He felt nauseous but it didn't take long for him to understand why. Arms and legs up, two monsters was lifting him with more or less difficulties. He struggled a little to free one arm and reached the hole in his head. Old habit. His hand crossed briefly the hole and he sighed. The scar was still here. Still no reset then. So what was happening ?

He rotated the head to look around him. The Royal Guard caught it ? They were in Waterfall ! That couldn't be good. And Papyrus ? Where was Papyrus ? Distraught, he lifted his head to see better who exactly was holding him. That was troubling. Even if he had sharp teeth and ridiculous shoulder pads, he swore that guy looked like his brother. Weird. He was insane, but not at the point he didn't remembered what his brother looked like the last time he saw him. And even if he was him, where the hell could he even find an armor like that ? All armors of the Underground were stored in the castle.

— Pap' ? he moaned.

« Papyrus » looked down in his direction, surprised to see him already awaken. His face got instantly cold and detached, almost evil.

— Shut up, Sans. I don't want to hear your stupid excuses right now. Sleep. You are… badly damaged. Even Asgore would be scared of you with a head like this.

— A… Asgore ? he replied, confused.

But Asgore died years ago. Why this sudden melancholy ? Sans got more and more the impression he didn't belong in this place. That feeling badly reinforce when his eyes turned towards the neck of the second person holding him. What the hell ?! He violently struggled, surprising his two carriers who dropped him on the floor. Sans evoked a bone wall and retreated to put the maximum distance between his brother, him and her. Panicked, he probed the ground to reach his axe. The bone wall consumed all his day magic in once. He wouldn't be able to defend Papyrus like that.

— The hell is wrong with h…

Undyne couldn't finish her sentence. To protect Papyrus, Sans jumped on her and went directly for her face. He hit her until his phalanges started to hurt. The fish lady tried to repulse him, completely lost, while his brother kept his arms dangling, too shocked by what was happening in front of his eyes to act and do something. The small skeleton planted all his teeth in his prey's shoulder, blinded by madness. Undyne screamed in pain as Papyrus finally reacted.

He grabbed Sans under the arms and dragged him back. The skeleton kept fighting fiercely and growling like an animal, his only eye injected with blood. A big red bone maintained it under the throat so Papyrus could hold him as best he could. Sans yelled like a lunatic, still obsessed with the idea to kill Undyne, whatever the price.

— Fuck this shit ! she yelled.

She invoked one of her spear and smashed it against the small skeleton head, as much for revenge as for knock him out. The effect was immediate and he fell inert in his brother's arms. Papyrus was out of breath.

The two royal guardsmen exchanged a worry blink. What in the world just happened to Sans ?