Helpful indeed

The start

Flipping through the pages of the third journal frantically, dipper desperately looked for something- anything that could help defeat bill.
He read page after page, but found nothing, until...

He landed on a piece of paper hidden in the middle of the book, it was written in invisible ink so he had to used the UV lamp to be able to read it, in it was a summoning circle and a few reversed words that he assumed were the summoning spell, no other information was  written tho.

Dipper was smart for sure, but in desperate moments like this, acting on impulse sometimes helped, which is why dipper recklessly started drawing the circle on the floor, it consisted of a star in the middle and a bunch of smaller symbols on the edge. When he was done, he started reciting the words, finding it a bit hard to pronounce a few of them...

After he the last word came out of his mouth, nothing happened, he waited and waited, but still nothing, he was about to give up when suddenly, a bright red light accompanied by some neon green fog started emerging from the circle, and before he could process anything, a figure was standing- rather floating in the middle of the star, it looked mostly human, minus the fact it's right eye and arms were covered in some thick black goo.

"Hello there kid!~" the creature said, it's voice kinda robotic like bills "why have you summoned me?"
Dipper, still in shock, mumbled something incoherent
"What's that? Speak up, I can't hear ya"
"I-i need your help!" Dipper spat
"What for? I need context"
"A dream demon called bill cipher is planning to take over the world and i need your help to stop him before it's too late!" He said quickly trying to explain as much as possible
"Ah good ol' Billy, doesn't learn from the past eh, well then, let's make a deal kiddo"
"A deal? You sure you won't trick me?" Dipper asked skeptically, he didn't want bipper 2.0 to happen
"Of course not, I'm a demon of my words, I'll help you defeat bill and in exchange, you get me a vessel, how does that sound?"
"A vessel? How am I gonna get you one?" Dipper was, to say the least, confused
"It's quite easy, just find a freshly dead body, that'll do" the demon said as if it was nothing
"A-a dead body!?"
"Yeah, unless you want it to be someone alive~" it smiled widely
"Fine fine, I'll find a way to get you a vessel!"
The demon stretched their arm out for dipper to shake
"deal?" they asked
"Deal" dipper hesitantly shook their arm, feeling the goo on it
"The name's MV by the way kid, call me when you need me, and remember, nothing is real this is all fiction follow me and goodbye!" With that they disappeared

Dipper stood there still trying to process the events of the past 5 minutes, he went downstairs and got out of the mystery shack, thinking hard about a way to get MV a vessel.

After walking around the forest for a bit, he finally got an idea
"MV!" He called out
"Calling me already? What's up?"
"You can teleport right? Can you teleport me to a cemetery far from here?" He asked
"Sure, grab on tight"
Dipper grabbed MV's arm waiting for something to happen, then he felt a sharp pain in his head and closed his eyes, when he opened them he was in a completely different place, surrounded by tombstones and plants of all sorts
"Where is this?" He asked looking around
"I believe we're in a country called Russia, it's quite pretty during the summer and spring isn't it?"
"Y-yeah, anyways, can you tell if there's a freshly hurried body?" Dipper asked, not believing what he was about to do
"Hmm yeah, that one over there"

He walked over to where MV was pointing and looked at the tomb, it was that of someone named Dominic, recently deceased due to an illness, judging by the writing on he stone, he should be about a few months older than dipper, but that's not important, he asked MV for a shovel and began digging, when the coffin was out he opened it and his nose was immediately hit with the smell of decomposing corpse, luckily, the body only had a few maggots here and there, no big damage.

MV, floating behind dipper, looked at the corpse examining it thoroughly
"Perfect!" Dipper was startled when they screamed in his ear
MV went rushing towards the body and disappearing right before colliding with it, after a few seconds of dipper just standing in complete silence, the body's eyes opened, and it spoke in MV voice
"Ah, good to have a human body, isn't it?"
"I-i guess?" Dipper said unsure
"Well, now that you're somewhat human, I guess I can introduce you to my family as my friend, that'll make it much easier for you to help"
"True, you wouldn't want your grunkles to know you've been going around making deals with potentially dangerous demons now would you?~" MV said, smiling menacingly
"But that's besides the point. Let me teleport us back to the mystery shack!"
MV, now in Dominic's body, grabbed dipper by the arm and before he could even react, they were already in front of his grunkle's house, they entered and saw that everyone (including Wendy and soos) we're in the living room, chatting and playing board games, talk about perfect timing, dipper nudged MV to make them stop smiling so weirdly and walked into the living room.

He exhaled "Hey guys, I wanted to introduce my friend here, his name's Dominic" he introduced MV using he dead boy's name
"Heya!" MV greeted happily