A Different Timeline (Short Underfell Fanfic)

Undyne's Grand Prank

Undyne was bored. So very bored. She didn't want to watch Mey Mew for the 20 millionth time. She loved Alphys, but the dino seriously needed to find something new.. Undyne rolled on her bed. "What to do!!!" She groaned. She was in the mood for a prank... but on who? Who would be an easy target and what should she do to them? The last time she pranked Alphys the scaled woman hid in her bathroom for days, doing stars knows what. Papyrus had burned down her first house for pranking him. Asgore was out of the question and the human was a dead man walking, they wouldn't live long enough for a prank. So that left... Sans. She grinned sharply. He would make the PERFECT target. Little shit wouldn't do anything but take it... but what should it be? She called Alphys and Papyrus to meet at the lab and talk, and don't bring Sans. They both agreed, sounding bored themselves.

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"WHAT NOW, UNDYNE." Papyrus growled. "I want to prank Sans, but I need ideas." Undyne replied. "Can someone like that waste of space even take a prank? Especially one of yours?" Alphys asked. Undyne waved it off. "I'll do something simple. Like make him piss his pants or something."
"THAT'S VERY EASY TO DO. IF YOU COULD DO SOMETHING THAT MAKES HIM GET OFF HIS LAZY ASS, THAT'D BE AMAZING." Papyrus grumbled, clearly annoyed. "Good luck with that, even if we died, he probably wouldn't do shit." Alphys huffed. That... gave Undyne an idea. "So what if we do die?"
"HOW AND WHY?"
"Hear me out guys. What if we get the human in on this for a few extra days to live. They can 'dust' us and we can see what Sans does next."
"HE'LL PROBABLY REJOICE.." Papyrus very well knew he was an utter asshole to Sans. It was the only thing he seemed to respond to, and even then, he barely did. He was curious though. So was Alphys. "I'LL RETRIEVE THE LITTLE BRAT." Papyrus left the lab with a flourish.

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Soon Frisk was being dragged in. They cringed upon a bone attack pinning them in place through their sweater. The three aggressive monsters towered over them. "Human, if you want to live, you're going to do what we tell you." Undyne growled. "W-wha-"
"You are going to make it look like you killed us, if you don't, we will kill you."
"IN THE MOST TORTUROUS WAY POSSIBLE." Papyrus added. While they could reset... Papyrus torture really WAS painful. "I-Ok... w-why..?"
"None of your fucking business, that's why." Undyne replied. "It needs a weapon. And we need a plan of action."
"W-wait! If you are really are doing what I think you're doing... I know how to make Sans believe it.." They replied quietly. The group looked at them in interest. "WE ARE LISTENING."

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They found themselves in Snowdin. Frisk got a knife from the brother's house and tucked in away. "Papyrus, I will need your scarf. The weather will getting bad soon, that will cover our tracks. We can hide behind the snowdrift over there." They pointed to a large snowdrift. "WHY THE HELL WOULD I GIVE YOU MY SCARF?!"
"Do you want him to believe it or not?"
"WELL YES BUT-"
"Just give them the damn scarf." Undyne snapped. Papyrus obliged. They put the scarf in the snow after slashing it about where Papyrus neck would be. "Go, go! He'll be here soon! So the group hid. A dangerous prank had just started.