From my list of Undertale Tickle Prompts on my Deviantart page. Undertale belongs to Toby Fox. I own nothing.

Prompt 22: Can't Prank Me
(Monster Kid and Sans; platonic pairing)

Monster Kid glanced around fast, a whoopee cushion in his jaws as he managed to nudge the cushion of the chair up and slip the device under it. Using his upper body, he put the cushion back in place, being careful he didn't set off the prank too soon. "Okay, whoopee cushions under the couch and chair cushions. Television remote velcroed to the couch arm. Mouthwash replaced with liquid cotton candy. Fake spider on the telephone. Looks like I'm done," he said to himself.

The small monster was attending a sleepover with Frisk at the skeleton brothers' home. Toriel and Asgore were away on business as were Monster Kid's parents, so the skeletons were watching over him and Frisk. He smiled as he thought about his work. He was eager to prank Sans, especially after the skeleton had gotten him and Frisk with a whoopee cushion the other day.

He tiptoed carefully back to Frisk's room and slipped into his sleeping bag, giggling to himself before he fell asleep.

The next morning, Sans had woken up early and when he got to the bathroom, he instantly smelled something sweet and checked until he found the mouthwash and smelled it. "Hmm, cotton candy?" He asked himself before noticing a small bottle of cotton candy mix in the trash. He smiled. "Oh, I see now."

Placing the mouthwash down, he checked to see what else had been messed with and checked under the couch cushions and chair cushions, smiling when he found the whoopee cushions. He did turn sharply at seeing the spider on the phone, but then saw it was a fake, which made him chuckle again before he noticed the television remote hadn't moved when he moved the cushions and he saw the reason for it. "Very clever, kid," he said to himself. "But unfortunately, I already knew."

A sudden, surprised cry filled the house and he rushed upstairs to see Papyrus leaning over the sink, his lower jaw covered in pink liquid and a splattered pink mess where the tall skeleton had spat out the cotton candy liquid in surprise. "Sans! What is this?!" Papyrus shrieked. "It's not the mint flavor at all!"

Sans put a hand to his mouth, holding in his snickers. "Nope, that's cotton candy mix," he said. "Someone switched it out last night."

"You, I'll bet," the tall skeleton grumbled.

Shaking his head, the pun-loving skeleton helped his brother clean up the mess. "Nah, but I know who," he said.

Papyrus rinsed his mouth out and sighed. "Well, I would like to catch whoever did so, but I'll be late in meeting Undyne," he said.

"Don't worry, bro. I'll catch them for you."

"Thank you, Sans. Oh, don't forget. Mettaton is picking up Frisk to take her to Alphys for her checkup. In fact, he should be here in a bit."

A knock came at the door just as Frisk and Monster Kid came out. "Morning, you two," Sans said. "Frisk, Mettaton's here."

She grinned, hugging MK. "Want to play some games when I get back?" She asked him.

"You bet!" The small dinosaur said. "Have fun with Mettaton."

"I will," she said as the robot lifted her up into his arms and smiled as he carried her to his limo and they got in.

"I'll see you and Monster Kid later, Sans," said Papyrus.

"Okay, bro. Take care," the short skeleton said.

"Please tell Undyne 'hi' for me, Papyrus?" MK asked with big eyes.

The tall skeleton smiled. "I will," he promised and headed out.

"Well, let's see what cartoons are on for ya," Sans said to the little yellow dinosaur, who perked up, but his face fell a little when the skeleton sat on the couch and the whoopee cushion didn't make a sound. Curious, he quickly recovered and sat on the floor in front of the couch. "Hey, why don't you sit up here on the couch?" Sans suggested.

"No thanks. I'm good right here," Monster Kid said.

"Are you sure?" The hoodie-wearing skeleton asked, sinking more into the cushions. "It's very comfy."

Now wondering if maybe he hadn't positioned the whoopee cushions right, the small monster tilted his head to the side before standing up. "Okay," he said, jumping up a little bit and squirming to pull himself up.

"Need a hand?" Sans offered gently, not wanting to offend the armless monster.

"No, thank you. I got it," the dinosaur said as he succeeded in sitting on the couch before scooting over onto the middle cushion so that he was sitting beside Sans, but no sooner had he begun sinking his weight into the cushion, a very loud sound filled the air, making him jump and land on his feet before he heard it again and realization hit him before he looked at Sans, who was smirking.

"What's wrong, kid? Something backfire on you?" He asked with a knowing smile.

Gulping, MK jumped down from the couch, but a blue aura caught him and he was pinned to the couch after Sans had removed the whoopee cushions and put them aside. "Nice try, kid. But you can't prank me," he said. "Although I have to give you kudos. Those pranks were really clever. Pap got the mouthwash this morning."

The small dinosaur looked sheepish. "Oops," he said sheepishly.

Sans smiled widely. "Now, you face the prank master's ultimate punishment," he said, taking a long feather out of his pocket and running it over MK's feet.

"Eek! AHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA!" The little monster laughed. "NOHOHOHOT THERE! HEEHEEHEEHEE!"

"Not there, huh?" The skeleton asked, his smile growing. "Well, that's too bad. Because those little feet are getting tickled, no matter what."

"AHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA!" Monster Kid laughed, squirming as much as he could with Sans' telekinesis holding him still for the most part. He laughed more as the feather moved over his bare feet faster and then tickling fingers came into the mix.

"Cootchie, cootchie, coo!"

Now the tickle torture was at its worst with the teasing words, making the small monster laugh harder before Sans paused a moment. "Now then, what about your ribs? Or your sides? Or your little tummy?" The skeleton asked.

"Nohohohohohohoho, pleaheeheeheeheease," MK pleaded through his giggles.

"Oh, yes," the joke-loving skeleton said. "A good tickle torture must include ribs, sides, and a stomach. Especially the stomach, but I'll get to that in a bit."

He now began gently poking Monster Kid's ribs and sides, wiggling his fingers masterfully and making the little one laugh crazily, his laughter becoming more crazier when his tickle torturer used his telekinesis to pick up the feather and use it to tickle his captive's feet again while his fingers went to work on the kid's sides and ribs.

"AHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA! STOHOHOHOHOHOHOHOHOHOHOHOHOHOHOHOHOP!"

"Nope."

At the skeleton's denial, MK tried another plea. "SAAHAHAHANS!"

"Nope, that's not going to work either," Sans said. "Now, let me have that stomach."

The small dinosaur completely lost it as the skeleton focused on the small stomach, blowing raspberries into it and his hands tickled it like crazy and even more feathers came into the mix with Sans' telekinesis, leaving the poor kid in stitches as the feathers tickled his other tickle spots and the skeleton didn't miss a single spot on his stomach, blowing a big raspberry right in the middle of it.

Squealing, Monster Kid tried to squirm free, but the telekinesis didn't let him go. "Tickle, tickle, tickle! I've got a very ticklish victim in my grasp," Sans teased him playfully.

The small, yellow monster let out another laugh before he lost his voice and coughed a little. The joke-loving skeleton stopped, but kept holding the kid in his telekinesis until MK got his breath back, giggling when Sans playfully poked his sides. "You want some more tickles?" He asked in a playful tone.

"No, please," the smaller one pleaded, looking at him pleadingly.

"Well…," his captor said slowly as he gave it a bit of thought and finally smiled. "Okay, I guess I can let you escape."

Monster Kid went to get up when his feet were caught with the skeleton's telekinesis again. "Or should I tickle these feet a bit longer?" He asked, his voice still playful.

MK shook his head. "Sans, please. No more," he pleaded.

"Okay," said the skeleton as he truly let the small monster up. "So, how about those cartoons for real?"

The armless monster agreed before sitting next to Sans, who wrapped the side of his coat around the kid, just like he did with Frisk before turning on the television so that they could enjoy the cartoons that morning.

I've never written a story with Monster Kid before, but when I was coming up with tickle prompts, I was like: "I've got to include MK too." :)

Please leave a review, but no flames!

GoldGuardian2418