As the Pines twins wake up and take their breakfast on what seems to be a regular morning at first, Dipper suddenly has a realisation as he was looking around the kitchen while eating...

"Oh gosh! Mabel!" He starts freaking out.

His sister gets startled and starts touching her face in horror. "What? Do I have a bug on my face?".

"No, it's not that! Look at the date!" He points at the calender in the kitchen, causing her to take a look.

She looks at it and doesn't really understand the reaction. "April 1st...? Why, what's wrong?"

"It's a prank day, and..." He looks around for a couple of seconds and then whispers in a paranoid way. "... and Bill might go loose..."

Mabel giggles at his behavior. "Don't be so silly! You know he's not that cruel anymore. What's the worst that could happen from childish pranks he might wanna pull off?"

"... You're not realizing how dangerous he is..." The brown-haired kid feels fear as he starts going to school.

"If you wanna know, I'm honestly more scared of what Alan might be like today..." As she says that, she feels some genuine discomfort just picturing it.

"Oh... right..." Dipper feels bad about that. "You could fake sick... Maybe I should too..."

"You? Lying in order to not go to school? Who are you and what have you done to my real brother?" She says that in a mixture of mocking and being surprised.

Her brother just gives up. "It's not right... Fine, let's go..."

The two reach the school, with Mabel not looking worried, and she notices. "Oh look, Sammy is waiting for us!"

She goes faster to join him while Dipper tells himself "oh dear...", being worried. He goes there anyway and realizes from a good look at the eyes that this is Samuel himself and not Bill, causing him to feel some relief.

Their friend looks very cheerful. "Good morning, friends! Ready to face the day?" He puts Dipper at ease. "High four, buddy!"

Dipper answers and as the hands touch, Dipper feels an electric shock causing him to scream and back down in one second. He then hears Bill's laugh and it's revealed that he put contact lens on to have normal looking eyes to fool him.

"What the heck?" Dipper gets mad.

"Oh, come on Pinetree, it's just a prank!" Samuel's body shows a big smile with hints of malice.

Mabel feels like giggling at her brother's expense. "Sorry, but yeah, you're overreacting."

"Thanks, Shooting star! By the way..." He takes something out of his pocket. "I got this flower for you!"

"Mabel, don't!" Dipper wants to warn his sister.

Mabel thinks "Oh, oldest trick in the book. I can handle some water squirt..." and approaches while faking to be naive. "Ooh, it looks nice!"

Bill activates a pump, causing a blue ink to squirt on her face, once again, immediately followed by Bill's laugh with a big grin. "April fools! Get used to it, you'll get this all day long!" He then enters the school, leaving Mabel with her ink spot on her face.

Dipper looks annoyed and tries to finds a way to wash Mabel's face. "Look at what he's done to you... See why I was worried?"

Mabel shrugs. "I still think you're being way too dramatic, Bro-bro! He's just having fun during a day about having fun... You should remember how he used to be if you think that's cruel."

Her brother frowns. "Yeah, I'd rather not remember..."

Mabel goes to wash the ink off from the nearest water fountain, but on her way there, she finds Samuel holding the faucet. "Here, I'll hold it for you...", he says to her, just before overshooting the water on purpose with a laugh and leaves.

Dipper is annoyed. "I told you... He's gonna be out of control the entire day..."

Mabel still wants to find positiveness in the situation, having washed her face. "And I'm telling you, this is a day about having fun with pranks... And these are harmless..." As the bell rings for them to go to class, she concludes before leaving. "Try seeing the prettier part of the picture."

Mabel joins class and she gets to hear some good news for her.

"It's too bad Alan isn't coming to class today..."

"I know right? He would've made this day one to remember! He's so funny..."

She sighs, feeling way better. Even knowing that Bill is probably gonna be in charge of Samuel's body for the whole day, this doesn't scare her nearly as much as what she just avoided.

Dipper joins his class and gulps when he sees Samuel waiting for him at the desk. He makes sure that he didn't put anything on his chair before sitting, but the smirk on his friend's face isn't reassuring.

Bill shows no regrets using his magic to cheat to pull many different pranks through the entire morning. For instance, he manages to tie Dipper's shoes together before recess, causing him to lose his balance completely. At recess, he's able to exploit stink bombs. He's also using many different items he can create on the spot, such as a mechanical snake to hide in Dipper's school bag, or getting Mabel to sit on a whoopee cushion..

And every prank is followed by Bill's joyful laugh as he's posing as Samuel to the other students.

The twins reunite for lunch, talking about the whole thing as they finish the main course.

"Bill is out of control..." reaffirms Dipper.

Mabel isn't as cheerful as she was earlier in the day. "Look, maybe he's taking it a little too far, but this is all harmless fun still... We can handle some pranks for a day, right? And if he annoys you so much, why don't you retaliate?"

"Mabel, I'm above doing this..." Dipper is bothered by the suggestion.

Mabel lists her brother's qualities like she did that dozens of time in the past. "Yeah, you're too honest, kind, against any kind of harm, loyal, trustful... But that's why you're easy to target!"

Her brother admits, but also adds. "You're a little too kind as well, aren't you? I'd like to kindly put him in his place, but I don't think this is the way to go..."

"Then please stop complaining about it if you don't wanna do it, because that's the only way to do so..." Mabel reaches for the small box containing the pastries they were given for dessert, only for then...

When they open the box, they see that Bill arranged a glitter bomb at the moment it'd be opened, causing the two to be completely covered. And the controlled Samuel wasn't far and has a huge smile on his face. "HAHAHAHA... APRIL FOOLS!"

After he left, Mabel stares at her brother with a slight frown. "Retaliation?"

Dipper coughes some confetti before answering. "Retaliation!"

And so, with Samuel being away, they quickly try to come up with a plan as they wash themselves.

"But how can we even do that...? He'd see it coming..." Dipper gets concerned.

She comes to a quick conclusion. "We probably have to attack him by approaching with something that makes him think he's on top. What would you say would be one of Bill's greatest flaws?"

Her brother starts thinking. "Um... His pride?"

Mabel is motivated. "Good call! We'll have to flatter his ego to make him feel overconfident, and strike from there!"

They silently plot together, getting some other students into it for help by saying they intend to take the most efficient pranker of the day down. They are a little concerned, but they are determined to give their prank a try.

And in the middle of the afternoon break...

They show up to Sammill with a measly done white flag. Mabel speaks loudly enough. "Sammy, we're here on behalf of most of the school's students to ask you... Please stop pulling these pranks on us. We recognize it, you are the king of pranks, and no one could possibly match you! We surrender to you..." She manages to sound utterly defeated.

Sammill smiles with a smirk. "Well, I'm glad to see that you have the decency to recognize my genius. I thank you for that."

Dipper pulls out a small fancy box from his pocket. "So please, accept this as a sign of us recognizing your superiority."

Bill is too blinded by his ego to think anything suspicious could be happening. "Aww, you're too kind, Pinetree... That's what your downfall is, after all..." And as he opens the box...

A flashing light gets him by surprise. "AH! MY EYE...!"

Dipper yells "NOW!", and thanks to the help of accomplices they got during the afternoon classes, who also fell victim to one of Samuel's pranks at one point or another, they managed to have him lose his balance with a rope as he backs down, causing him to fall on the floor. And following that, he gets hit with a bunch of water balloons, finishing with Dipper and Mabel getting paint splashed on Samuel. And as Dipper offers his hand to help Sammill stand up, he feels an electric shock, much like what he did to his friend in the morning.

"You are indeed king, Sammy..." She moves closer so she doesn't get heard by anyone else "Or rather... Mr. Bill Cipher..." Says Mabel confidently.

"The king of fools!" Adds Dipper.

The two fist bump and Bill makes Samuel smirk in a way that says "I'm really proud of you...". He stands up and speaks louder to everyone who participated in this plan. "Everyone... I kneel!". He graciously bows in front of everyone.

After some laughs at his expense, Dipper and Mabel go to reach him and speak. "Thanks everyone! We all got our retaliation, and now, April Fools is over!" Every kid who participated talked to Sammy about this, none of them knowing that they're actually speaking to a mischievous demon. In short conversations, both sides respect each other and agree to end the pranks.

At the end of the school day, Sammy stands in front of the twins. "Pinetree, Shooting star... I never thought you'd succeed at beating me when it comes to mischief... It sounds weird, but... I'm really impressed with what you managed to do!"

Dipper frowns. "Bill, you went a little too far with your pranking! Although... You might've cheated, but you never did anything too horrible or harmful..."

Mabel smiles. "So we don't really have a reason to hold it against you! Even if not all of it was much fun..."

Bill exclaims cheerfully. "April Fools is such a great human tradition! I'd love for it to take place the entire year..."

"NO!" The twins react together, horrified.

Bill giggles, knowing what the reaction would be. "Thank you for this awesome day! I've had such a great time!" He then gives up on the body's control, letting Samuel get consciousness, for the first time since the previous day. He looks completely disoriented.

Dipper and Mabel quickly hug Samuel as an apology for using his body to prank Bill. The kid is a bit lost as he feels his clothes soaked and dirty, and some pain in his eyes. He has a quick discussion with his friends about it, revealing that they did this because of Bill before they part ways.

On the way to their home, Mabel brings up something that's on her mind. "I feel a little bad. Samuel didn't do anything... Yet at the eyes of everyone else at school, he was the cruel one who was mocked..." The thought of it makes her uneasy and a little sad.

Dipper answers, trying to reassure her while saying what he truly thinks. "Yeah... But see it this way... Those were just pranks Bill did through Samuel. To the eyes of others, he was just having fun today. And us pranking him back was in that spirit too. You've seen afterwards that Bill took it well and that there were no hard feelings between him and the other kids he pranked. I'm sure that starting with tomorrow, no one will even see our friend in a bad way."

Mabel nods, agreeing and hoping for her brother to be right, even if she can't completely shake those feelings off.

Samuel reaches home and his appearance gets noticed by his parents, which he quickly explains as "April fools shenanigans". He goes to the shower and gets new clothes. After which, he locks the door of his bedroom, looking annoyed.

The demon appears in the room with a satisfied expression in his eye. "Hey, Fuzzball, what's up?"

Sammy isn't in the mood for games right now. "What did you do today?", he asks with a stern look on his face.

"It was April Fools! The answer should be obvious!" The triangle demon returns the mood of the kid.

"Did you harm my friends? Did you get me in trouble? Did you...?" He has many questions that get cut off.

Bill gets his cane of and makes an arm gesture with it. "Easy there, Fuzzball... Everything I did today were harmless pranks you meat sacks tend to do. I didn't do anything cruel that you heard I was able to!"

Samuel trusts him when he says that as he sounds sincere, but he gets worried. "But if you spent the entire day pretending to be me and pulling all sorts of pranks at school, I'm gonna get hated, no...?"

Bill acts cheerful about it as he floats all around the human. "It's a day where it's expected to pull mean pranks, you're fine!" He stops to face him and lets out a giggle at the thought of what happened next. "Besides, your friends got revenge!"

He gets scared. "On... me...? You mean they pranked me to get you?" Sammy starts blushing of shame about it. "I was pranked... In front of the whole school... Thanks to you?"

"Yup!" Bill states proudly. "Pranks were for me, but your body and yourself took it for anyone that isn't your two friends."

Seeing the kid's expression, Bill extends his arm lenght to touch his shoulder. "Don't feel too bad, Fuzzball! It was just a day of games for everyone involved. And I'm proud of your two friends for getting back at me! They know it was me and not you, and no one at school is hating on you for enjoying the day's traditions! No one was hurt, and you aren't hurt either, are you?"

Samuel starts admitting. "Well... no..."

"Then there's nothing to be scared or ashamed of! Tomorrow, everyone will move on from that! Besides, isn't that what you three wanted for me...?" He looks at his bracelet for a bit. "You wanting me to find fun mischief that isn't evil? Wasn't today a success in that?"

"..." He starts having a faint smile. "I guess you got a point..."

"Of course I'm right!" The demon goes back to acting proud. "And if you doubt me, just ask your friends!"

Sammy suddenly starts thinking. "You know... You always manage to be convincing... That's a huge quality!"

Bill looks smug from that. "Yeah, I'm very smart! Didn't you figure it out by now?"

This obversation he just made gets the boy thinking and making the connection with Bill's old ways. How he could get a deal to be made thanks to setting up the situation and managing to say the right lies at the right time.

"What's up, Fuzzball?" Bill is looking curious.

However, Sammy doesn't want to bring this up in case it ruins the mood, and he finds an excuse. "Um... I've been thinking... About the kind of stuff you like... You know, that scary, nightmarish stuff you love so much!" He feels like he'd regret what he's about to say, but goes through with it. "I wouldn't mind seeing more of it. Maybe I'd get the appeal this way..."

This gets the triangle really excited. "Oh, with great pleasure! I can show you stuff, creates creepy things around just to showcase what I can do! I could made it happen here or when you sleep! How about...?"

His human partner gets a little scared. "Easy, though... I don't wanna be traumatized or anything like that... Maybe let's start small of the scare scale..."

With that being said, Samuel's evening is spent having Bill showcase his appreciation for the spooky and nightmarish, which he's actually presenting as amusing and admirable. True to his words, he's starting with just mildly scary things suitable for a 13 years old. He's disappointed when he's asked to stop, like a kid who can't showcase all his toys at once. But regardless, the two of them manage to have a fun evening and early night in spite of the odd choice of topic.

Author notes: Yup, you probably saw it coming... Bill in a human body during April Fools Day just writes itself. So much so that I actually planned parts of this chapter far in advance. I hope it was enjoyable.

Thanks for reading!