"AHAHAHAHAHA! Pine Tree, you won't be able to save this world n-" Bill starts, before being cut off by the sound of about 7 different portals opening. "Eh?"
"Hey Bill! Remember us?" A voice says, as 8 people step out of the portals, one of them prominently in front of the rest.
"I… impossible! The Multiversal Guardians?!" Bill shouts, stepping back.
"Eeeyup. And guess who!" the voice says, and everyone looks at the young girl in front of the rest.
"Who… who are you?" Melanie asks. At that, a boy of about 19 years steps up next to the girl.
"We're just some passing through Kamen Riders. REMEMBER THAT!" He says.
"HENSHIN!" 7 of the 8 shout, and put in locks/usbs/cards/coins/rings into the belts on their waists.
"Ptera, Tricera, Tyranno! PuToTyraSaurus! Cyclone! Joker! Kamen Ride: Decode! Kamen Ride: Decade! Flame… Please! Soiya! Orange arms! Hanamichi (The path of blossoms), on stage!" The belts announce. A bright light flashes, blinding everyone. After it passes, the 7 who activated their belts were now changed, with the 7th fainting. The first is now covered in a white bodysuit with purple, dinosaur themed armor. The second is split down the middle, the left half being black with purple highlights, and the right half being green with metallic yellow highlights. The third is covered in a yellow and black armor with cyan, bug like eye lenses. The fourth wore a similar armor, only in magenta with green eyes. The fifth is covered by a black bodysuit with a black long coat, and a helmet that has a large ruby at the front. The sixth resembles a samurai, with a blue bodysuit and orange themed armor on top, with an orange slice on her visor.
"A girl? Your leader, is a little kid?" Bill scoffs.
"Ok, first, not their leader. Second, don't recognize me, Bill? You really should. Don't you remember that deal you made so long ago?" The girl retorts, blue flames appearing on her hand.
"WHAT?! Bu- but I got rid of Wheel!" Bill shrieks, obviously shocked.
"Ok then fine. Maybe you recognize the name Murphy?" The girl says.
"Wait… like Murphy's Law, Murphy… or?" Dipper says, confused.
"That's the most prominent use of my last name, yes. Besides… Maybe this will refresh your…. failing memory." she says, and says exactly one sentence: "You don't realize the downsides of making deals with multiverse travelers." At this, Bill falls down, obviously shocked beyond belief.
"Ok, just WHO are you?!" Melanie asks the girl.
"Why… you really need to start listening. In case you didn't know, most multiverse travelers are from the same world. THE ONE WHERE YOU LIVE." the girl says. "The name's Sarah Murphy, and well… Bill made the mistake of making a deal with me… In another universe of this world… the original Gravity Falls universe. By coming here, girl, you have made this another universe in the multiverse, causing thousands of problems in the multiverse. And well… Let's just say I don't like seeing universes destroyed…." Sarah says, looking at Decade and Decode, and then pulls out a belt that looks like one of the ones that the black and green rider is wearing, but with only one slot instead of two. She puts it on, and then pulls out a USB drive. She hits a button on it, causing it to announce: "Ender!" She puts it into the slot, and then flips the slot out. "Henshin." she says.
"ENDER! UPGRADE! DRAGON! BURN, BURN, BURN BURN BURN!" the belt announces, and another blinding light flashes. When this one disappears, Sarah is in armor that looks like a dragon, complete with wings on her back, and a dragon themed helmet.
"Now then, Bill. Are you gonna attack, or what?" Sarah scoffs.
"What do you think, Wheel?!" Bill says, and then to Dipper, Mabel, Stan, and Melanie's disbelief, shouts, "ATTACK!"
"Wait WHAT?!" Dipper shouts.
"END'S BANE!" Sarah shouts, and a sword appears in her hands. "Surely you remember this, don't you, Bill?"
"You must be kidding me, Wheel! A sword? What good will that do for you?" Bill says.
"Plenty more than you think!" She says, and then shouts in perfect Japanese, "COUNT UP YOUR SINS, BILL!" (I ain't gonna bother putting that in Japanese.) She runs at him, the sword pointed directly at his (non-existent) chest.
"HYAH! IKUZE!(Let's go!)" She shouts, and the rest attack the army. "I'm dealing with you! You and I, we have some… unfinished business…" She says, with the raise of a hand. She slashes at him, causing him to back up.
"Wha- what do you mean?" Bill says.
"I mean… You really should start cleaning up your messes. We figured out it was you causing those multiversal disasters PRETTY quickly. And by the way… girl! I do believe you have something that you want to stop from happening?"
"Who? Me?" Melanie asks.
"Is there any other girl here besides me and my friend Jess?" Sarah says, pointing at the girl in orange themed armor.
"Uhhh no?" Melanie says, clearly confused.
"JUST GET OVER HERE!" She shouts.
"Okay Okay, Jeez!" Melanie says, running over there through the battlefield of humanoid demons and Kamen Riders in combat. Sarah simply takes the usb out, before pulling out a diamond shaped bracelet like object.
"Henshin!" she says, sliding a card through.
"Change: DREAM DEMON!" the belt says, and she turns into some sort of wingless dragon, wearing… well basically what Dipper wears, aside from her fedora, with a wheel symbol on it.
"Tha- that's the name Bill called you! Wheel!" Melanie says.
"Well no S*** Sherlock!" She scoffs. "Now… Hey RED! Ya still here, or do I need to summon you?" At this, a guy in a red vest and gray shorts appears, but somehow floating.
"Ya called, S?" Red says.
"Don't… call… me… S! Now then…. YA READY TO MAKE A DEAL! Owwww throat that hurt…" She says, holding out her hand, blue flames enveloping it.
"Ready!" He says, shaking her hand. Suddenly, she's in his… body? I don't even know what he is at this point.
"GAME ON!" they both shout at the same time, and Megaman-like armor appears on Red's body.
"What is this… POWER?!" Bill shouts.
"How can you not remember this? Don't you remember the land of MINECRAFTIA? Honestly, you and your failing memory." Sarah scoffs. "Now then, gi- or should I say, Bookworm?" She says, a smile on the showing part of Red's face.
"What?" Melanie says.
"How do you know that, Wheel?!" Bill asks.
"Simple. I've been watching this universe, waiting for the right moment to come help you with your… problem. Hehehe, sad thing is, Bill here tried to close off the portal link I keep in my dorm in the base… He failed, because I was able to open enough portals to get every single multiverse traveler here."
"Now then." She says, pulling out a ring and putting it on her right hand. She puts it against her waist and a belt appears.
"Connect, please!" it says, and a portal opens.
"WOAH! What the?" Bill says, never having had the chance to see this. Sarah simply pulls a card and belt out from the portal before taking the ring off, causing the portal to close.
"Catch!" She says, throwing it to Melanie.
"What is this?" Melanie asks.
"A driver. Put it on your waist, open it, insert the card, say Henshin, and close it." Sarah instructs.
Melanie does that, and the belt announces, "Kamen Ride: Blank!" A blinding flash later, and Melanie is in armor not unlike Decode's armor, but entirely in shades of black and gray.
"What in the?"
"Hey, just like the song: We are the heroes of our time!" Sarah says, smirking… or is that a genuine smile?
"Huh? What… What is this… power you hold? I sense magic beyond anything I've ever encountered in you.
"Hey, a wizard never reveals their secrets in front of their enemies! Now then, you ready to take down this fool of a dream demon? I've encountered him two too many times in my travels, so I'm glad that I can be rid of him!" Sarah says, still smirking.
"Now then! Here! Take this card, and put it in the driver!" she says, handing Melanie a card with the words "Final Form Ride: RED ADVENGER!"
"Red… Advenger? What does this… mean?" Melanie asks, putting the card into the driver, causing the belt to announce, "Final Form Ride! R-R-R-RED ADVENGER!" Suddenly, Sarah is gone, and replaced with an arm cannon on Melanie's arm. "WHAT THE?!"
"Hey, that card made it so I'm a weapon. Final Form Ride does that!" a voice says from the arm cannon.
"Woah… dude that's…. really weird…" Dipper says from behind them, blocking the attacks of the demons.
"Hey, us riders get used to it, our boss does the same thing." She says, causing the arm cannon to point at the one with the Kamen Ride: Decade card inside their driver. "That's The Destroyer of All Worlds, Kamen Rider Decade, even though he doesn't destroy many. His protégé is the Kamen Rider Decode, aka my brother." Again the arm cannon moves, pointing at the boy from earlier. "Now then! Shout 'Red Advenger Finale', and that will activate the finisher." She says.
"Red Advenger Finale!" Melanie shouts, and the cannon starts charging.
"On 3, shout Fire!" Sarah says. "1… 2…" the cannon now has a massive ball of energy on the end. "THREE!" Sarah shouts, and both her and Melanie shout, "FIRE!" causing the ball of energy to go straight at Bill Cipher. The ball of energy hits Bill.
"NOOOOOOOOOOOOOOOOOO!" Bill shrieks, dissipating into little yellow particles, and a card appears in his place.
"Take out the card." Sarah says. After Melanie does that, Sarah is back, As well as Red Advenger, and they are in their respective bodies. Sarah picks the card up and puts it in her pocket.
"That takes care of Bill! Now for the army!" Sarah says, running at a demon before flipping the usb again.
"ENDER! UPGRADE! DRAGON! BURN, BURN, BURN BURN BURN!" The belt announces, and by the end of the flash, the demon is on the end of her sword.
"DECADE! Plan 123ac!" She shouts, and the one called Decade nods.
"Plan 123ac? What's that?" Dipper asks, dodging a blow.
"You'll see! It's for extreme situations only!" Sarah says, and then nods to her brother. "NOW!"
"Attack Ride! Portal!" His belt announces, and then Sarah calls into the portal, "Hey W! I'm calling in my favor!" At this, 2 people walk out.
"Okay then, Philip, Shotaro? Do what you do best!" Decode says.
"Hey, took ya long enough to call that favor in!" One of the two says.
"Hey, I told ya Philip, plan 123ac is for extreme emergencies only!" Sarah says. The other one, Shotaro says, "Hey Philip! Ready?"
"Always!" At this, they pull out two USB drives like the ones from earlier, and a bird like object flies over them as they push the two USBs into their own belts. The USBs then release trails of light, which the bird like object lands on and slides into his belt, before opening up to reveal a turbine inside marked with an X.

"XTREME!" A jingle plays as the two people merged together, becoming covered in an armor split into three sections. The right section is green with gold highlights, the middle is gold, and the left black and purple. 6 golden insect wings appear on his back. "Well then, ready Decade?" Sarah asks him.
"Of course I am! What, you think I WOULDN'T be ready?" Decade scoffs.
"True." She says.
"Now then!"
"ACTIVATE PROTOCOL 123AC, EVERYONE!" Sarah yells out. One of them, the orange themed rider, says,
"WAIT WHAT?! I'M NOT READY!" Sarah approaches her.
"You've been ready, you just never believe in yourself. Now then!" She says, pulling a card out, and throwing it to Decode. "3..." Decode says as he catches the card.
"2..." Decade says as he gets into position.
"1..." W says as he flies down.
"GO!" Sarah yells at everyone.
"Final Form Ride! D-D-D-Double!" The belt announces as Decode grabs W and literally SPLITS HIM IN TWO.
"Oooo ouch... that does NOT look pretty..." Melanie says.
"Ya know, the funny thing is, they don't feel anything besides a slight tingle." Decode says, as he looks at the now two halves of Double.
"Fruits basket!" Is heard by everyone.
"Hension!" Everyone else yells, and pull out their final forms.
"Kuuga, Agito, Ryuki, Faiz, Blade, Hibiki, Kabuto, Den-O, Kiva! Final Kamen Ride: Decade!"
"Kumoki, Avius, Koa'ki, Alpha, Coppe, Shizuneki, Arachnia, Chronos, Legend, Ace, Re:Birth, Astro, Eclipse, Zen, Soar! Final Kamen Ride: De-De-Decode!"
"Ender, Starlight, Flare, MahouShoujo! Final Kamen Ride: R-R-Roll!"
"Lock Open! Kiwami Arms! Dai-Dai, Dai-Dai, Dai Shogun!"
"Super Super Super! Super Taka! Super Tora! Super Batta! Su~per TaToBa TaToBa! SUPER!"
"Fang! Joker!"
"Infinity, PLEASE! Hi Su Fu Dou, Bou Jaba Byun Dogan!"
Cue giant flash of light! After said flash passes, everyone sees that the riders are in their final forms.
"Double! Round up the army!" Sarah orders, and W nods.
"Come on, follow the flying bugman!" 2 voices say from the suit as he flies around the army. After about 5 minutes, they are all clumped together.
"Everyone ready?" Sarah asks.
"Ready!" 8 other voices shout.
"8... RIDER... KICK!" They all shout as they jump up and kick the entire army, taking them out as they land on them.
"Welp. That takes care of that!" Sarah says as she brushes the dust off of herself. "Everyone, clean up please!"

~After the Battle~
"Ya know, I didn't have to help ya." Sarah says, watching the rest of the Multiversal Guardians clean up the mess.
"What do you mean?" Dipper asks her.
"Simple. In another version of this dimension, Bill offered to make a deal, you and Bill would switch, you being a dream demon, him being human, in your body, and he would completely stop the battle. But then, little Melanie over here, stepped up and shook Bill's hand, and then they had to make a separate deal because that deal was meant for you. Bill had to make his own human body, and Melanie, had to make a dream demon body. As well, Bill erased your memories of his name being attached to the dream demon, and he added memories of being your friend for 2 years here in Gravity Falls. Kinda confusing, but kinda boring, in terms of what I've seen." She then motions to the 19 year old boy. "YO! DJ! GIT OVER HERE!" She yells at him.
"I thought we agreed on code names!" DJ says.
"Code names are boring, and hard to remember. DJ isn't." Sarah says.
"Wait! How do you know all that stuff about an alternate version of this dimension?" Mabel asks Sarah. Sarah then looks at her hands, as if inspecting them.
"Let's just say…. I have a couple… contacts. Right, Bill?" She says, pulling a card out of her pocket.
"LET ME OUTTA HERE, WHEEL!" Bill's voice comes from the card.
"WHAT THE?! I thought you destroyed him!" Melanie says.
"You can't exactly DESTROY a dream demon, Melanie. What you CAN do, though, is trap him in a Rouze Card." She says, showing them the card.
"LET. ME. OUT. WHEEL!" Bill says again.
"Not happenin, Bill, old pal. Oooooo the fun I'm gonna have with your form!" Sarah says cheerfully.
"What do you mean?" Stanley asks Sarah.
"How about I show, rather than tell. DJ? Golden Joker?" Sarah says, and DJ nods.
"You got it." DJ pulls out a playing card with a stone color to it, and the word Joker written in gold on the upper left and bottom right corners of the card. A heart shaped buckle appears around his waist, with the heart being a sickly green color. He swipes the card through the middle of the buckle, and becomes covered in black static. After a moment, he emerges, changed into a demonic looking humanoid with blades sticking out of nearly every portion of his now purple body. "This is what Rouze Cards can do. If you happen to be a Joker, like myself, you can use a Rouze Card to take on the form of the creature sealed inside the card, and use their powers as if they were your own."
"Which would be even MORE fun with a dream demon, such as myself!" Sarah says.
"Wait… back up. Where'd all this tech come from?" Stanford asks, looking at the belt.
"Let's….. NOT delve into that topic…. Wait…. When'd you get here, Stanford?" DJ asks.
"Sometime during your fight with Bill." He says. "The portal my brother fixed," He says, pointing at Stanley, "brought me back." Sarah pipes up after he finishes saying that.
"How about y'all tell me how you're gonna get Melanie here," She starts, pointing at Melanie, "Home? I had to cut off all exits so I wouldn't have interference with this battle. We have a couple of enemies who would very much like to work with Bill here to destroy the multiverse… We don't want them here, now do we?" She finishes, holding up the Rouze card to emphasize her point.
"Wheel, if you let me out, I prom-" Bill starts before being shoved into a card box.
"Zip it, buddy." She mutters.
"Now then, shall I introduce the crew?" Another voice says from behind them.
"OH! Ummm… Hi Boss…" Sarah salutes, before shrinking down. "Don't kill me please!" She mutters.
"I'm not gonna kill ya, Roll! Jeez… You ALWAYS expect the worst…." Her boss says, before motioning to the others.
"Let's see here. Oh! I am Tsukasa, otherwise known as-" He starts, before being cut off by Melanie.
"The destroyer of All Worlds. Ya know, never thought that would be a thing…."
"Ohhhhh it is! And here's the funny thing! I don't really destroy many worlds. So, yeahhhhh…. Well then, onto the girl over th-" Tsukasa starts again, before being cut off by Sarah this time.
"Boss, lemme handle this." She says, and points to the girl. "Yo, JESS! Come on over! You too, W, Wizard, OOOs, whoever I'm forgetting…" She calls out.
"Yo?" A girlish voice says from inside the W armor.
"Oh yeahhhh... kinda forgot you were with us, Anne-Marie... hehehe sorry..." Sarah says, her hand on the back of her head.
"This is Anne-Marie, Jessica, Blake, and Tim." She says, pointing at each one respectively.
"Hello Homosapien!" Jessica says.
"Sup." Blake replies.
"Umm... Hi?" Tim says. Sarah just face palms at Tim.
"How many tim-" Sarah starts before being cut off by DJ.
"Not the time. You gonna stay here, make sure no others come?" DJ asks her.
"Yeah, close off every portal except mine again please." Sarah orders.
"Got it, Sarah!" Jessica salutes.
"Decade, do I have permission?" Sarah asks.
"Permission granted."
"Everyone, MOVE OUT!" Sarah orders.
"Yes ma'am!" Everyone except Decade yells, and runs into a portal behind them.
"There's that taken care of... now onto the protection..." Sarah says after they are all gone.
"How long will you be here?" Melanie asks.
"As long as it takes..." Sarah answers.

"... Well well well... where will our heroes appear next? See the thrilling details of their adventures to protect that world in "The Multiversal Guardians!" By Firetype55!" A voice says in another dimension.

Disclaimer: this chapter was written by Firetype55 with help from Piplupm