All of the suggestions I received were amazing! I think I'm going to use most of them and they inspired me to update this fic super fast. I haven't been this inspired to write in a very long time. It's that new fandom feeling. I missed it!

Chapter Two: A Declaration

Sans was fairly certain he would be able to figure out what kind of revenge Papyrus would dish out once Frisk and Undyne had left the house. But Papyrus had been uncharacteristically quiet, something that never boded well. If there was one thing Sans knew about his brother, it was that silence was highly suspicious. So when Papyrus went on a late night grocery run, Sans snuck into the kitchen to check out what he had bought.

More spaghetti sauce and noodles. So maybe there wasn't revenge coming his way.

Still, Sans felt a bit on edge and, as an extra precaution, locked his room up tight. By the next morning, he was fairly sure he was overreacting. Papyrus wasn't a prankster at heart. He was far too obvious. And forgiving.

As usual, Papyrus was up quite early, newspapers spread out in front of him. He didn't look up when Sans walked in, yawning and stretching.

"I assume you had a nice nap." he said shortly, turning the page.

"Pretty good." said Sans.

He opened the fridge a tiny smidgen and peered inside. There was nothing unusual in there. No bucket of water over his head that would drop on him were he to open the door any more. This was promising.

"So," he said, taking out a bottle of ketchup from the door of the fridge, "no hard feelings about last night?"

"Water under the bridge." Papyrus shrugged. "You know I can't stay mad at you."

"That's one of the many things I like about you, bro. Your forgiving nature." Sans said with a grin.

He took a huge swig of ketchup and proceeded to spit it out. His mouth suddenly felt like it was on fire.

"What the-" he popped off the cap and looked into the bottle. "What's in this?"

"Oh, you like it?" Papyrus reached into his pocket and drew out a little bottle. "I thought my extra ingredient would add a bit of flavor."

Tears streamed from Sans's eyes. He threw open the refrigerator door and grabbed a half empty carton of milk, opening it and taking a huge swig. This, too, he spat out.

"It's sour!" he bolted to the sink and stuck his head under it, pouring water into his open mouth. "Why would you-"

"I've told you not to put the milk back in the fridge when you should be throwing it away instead." Papyrus said nonchalantly. "Serves you right."

He tossed the bottle over to his brother, whose head was now completely soaked. Sans looked at the little label.

"Ghost pepper hot sauce?" he wheezed.

"Well the man at the store was very helpful and said it was the hottest they had." Papyrus leaned on the table a bit, clearly enjoying the spectacle. "That should teach you not to mess with me, The Great Papyrus! Nyeh heh heh!"

"You, sir, are playing a very dangerous game." Sans withdrew his head from the sink, eyes still watering. "There will be consequences!"

"Well at this point, it's nothing I haven't dealt with before already." Papyrus chortled. "Not as fun from the other side, is it?"

"You think I've used the full extent of my abilities?" Sans's blue eye gleamed. "You have no idea."

Papyrus turned back to his newspaper, not concerned about the mess Sans had made in the kitchen. He would clean it up later. Meanwhile Sans dug in the fridge for a fresh carton of milk. Underneath the table, Papyrus texted Toriel:

"SUCCESS!"

As Sans poured milk all over his mouth and, indeed, his face, Toriel quickly replied:

"It is not over yet."

After a quick, cold shower, Sans opened his closet and reached in for his hoodie. His hand met midair.

"Papyrus!" he bellowed. "What did you do to my hoodie?"

No answer. Evidently, Papyrus had left the house. Grumbling to himself, he opened his drawer to get out something else to wear. Much to his irritation, a different sight met his eyes.

"Ohhh he is going to have a bad time." Sans muttered angrily as he pulled on the only shirt available. "A very bad time!"

Twenty minutes later, Sans secured his bicycle and entered Grillby's. Everyone inside was laughing about something, though he couldn't quite see what.

"I'm going to need something extra strong to-" Sans began when he finally caught sight of the group sitting up at the bar.

It was a very strange sight. There was Papyrus, grinning triumphantly. Beside him was Toriel and... himself. Someone just about his size in his hoodie.

He only had a split second to stare before the figure in his clothes turned around and grinned at him. It was Frisk, looking very amused.

"Nice shirt." she said with a giggle.

Sans looked down at the blue and pink striped shirt he was forced to wear. While it looked quite cute on Frisk, it looked ridiculous on him.

"Ha. Ha." Sans opened his arms wide, showing off the shirt. "Yeah, go ahead. Laugh at me. It's what I'd do!"

"Come. Sit." Frisk patted a seat next to her.

Sans gave her a suspicious glare before walking over to sit on the stool. A loud, rude noise drowned out the nearby conversation and several people around them began to laugh harder.

"Careful, kid. Sometimes people put whoopie cushions on the seats." Frisk said, a mischievous glint in her eye.

"Oh very funny, kid. Let me guess, my brother put you up to this." he glanced sideways at Papyrus.

"Actually," Frisk turned to Toriel, "it was Mom's idea."

Sans stared at Toriel with wide eye sockets. "Oh really?"

"Well you can't be the only one to have all the fun." Toriel shrugged.

"You're outnumbered, Sans." Papyrus chortled. "You might as well give up and leave your practical jokes in the past."

"You just wait, Pap." Sans said, his mind whirring with ideas for revenge. "All right, Grillby, I'll have an order of fries."

"It's on me." Frisk said in an uncanny impression of Sans. "Just put it on my tab."

"All right, that's pretty good." Sans admitted. "Now give me back my hoodie."

With a shrug, Frisk handed the hoodie to Sans, who immediately put it on, mostly to hide the ludicrous striped shirt he was forced to wear. When he put his hands in his pockets, a weird squeaking noise emanated from it. He extracted two rubber chickens.

"Heh heh heh, all right." he shook his head, smiling at the joke. "If that's the way you want to play it."

He heard Papyrus's triumphant laugh and decided that revenge would be sweet.

After a long day, Papyrus liked to watch Mettaton's game show with a frozen treat. He liked Nice Cream a lot and always kept a hidden stash. He had left Grillby's hours ago and Sans still wasn't back.

The second Papyrus opened the freezer door, he heard a loud squelching noise and was propelled backward by something cold and white. Wiping the substance off his face, he saw an empty Gaster Blaster sticking out of the freezer, dripping with vanilla Nice Cream.

"Smile!" came a voice just outside the window.

Papyrus looked over to find Undyne filming the incident with her phone. Flinging Nice Cream off his hands, the skeleton narrowed his eye sockets.

"Fuhuhu!" Undyne cackled. "This is definitely going on youtube!"

Papyrus stared at the kitchen, its floor now covered in the Nice Cream. He would have taken another stupid prank as revenge. But this wasn't a stupid little prank. This took effort. This took an accomplice. As he tried to stand up, his feet slipping all over the mound of Nice Cream, he glared at the window, where he could just barely make out Undyne running away.

"This. Means. War."

And it begins! Special thanks to deadlyswarm, AceLegends, and NRMania for your ingenious prank ideas! Keep them coming and I'll keep the chapters coming!

Don't forget to review!

~KateMarie999