Hello, internet! Welcome to my very first Undertale-Gravity Falls crossover. Truth be told, this is something that I've been toying with for quite awhile now, and at long last, it's ready to be put into production. Well, let's get this show on the road!

DISCLAIMER: I DO NOT OWN GRAVITY FALLS OR UNDERTALE. THOSE BELONG TO ALEX HIRSCH AND TOBY FOX RESPECTIVELY. BUT YOU KNEW THAT ALREADY. ALSO, THE FOLLOWING STORY CONTAINS THE BEST SPOILERS YOU CAN FIND ON THIS SIDE OF THE DIXIE LINE FOR BOTH THE PACIFEST AND GENOCIDE RUNS OF UNDERTALE. YE BE WARNED!

Chapter 1: The Boy In The Woods

My name is Asriel Dreemurr. I am the former Prince and heir to the Underground Kingdom, the God of Hyper-Death, and ordinary teenage human boy. Yeah, how ordinary does anything I just said sound, right? Well, I certainly wouldn't have believed it myself, especially after everything I've done. I'm sure if you've heard of me, you probably know what I've done. But, for those of you who haven't, I'll explain it to you. After my initial death at the hands of humans back in my dimension, I was reduced to nothing more than a mere flower. Then, the Royal Scientist, Dr. W.D. Gaster and his assistant, Alphys, injected me with Determination. And before anybody says "Pfft, you CAN'T inject anything with DETERMINATION, Determination is an emotion!" Trust me, yes you can. Although, it has the tendency to cause monsters to, uh… melt and distort. If a monster is lucky, they'll only receive some permanent scarring. If not, then… you'd either better have a mop handy or else… you don't want to know. In any case, the Determination revitalized me. I took the alias of Flowey the Flower and… look, the citizens of the Underground were all actual monsters but me, as Flowey… I was pure evil. I pushed Dr. Gaster into his Determination Extractor, melted and disfigured him to the point that he fell into the Core in his pain. The Core provided sustainable power for the Underground, by the way. During my tenure as Flowey, I made everyone's life a living Hell, all so I could get control of the timeline and destroy it.

And I hated it. I longed to become Asriel again.

Then, one day, a human named Frisk was able to save me from the monster I'd become. Thanks to her, I was able to get my vines on the six Human Souls that were needed to break the Barrier that kept us trapped and absorbed them into myself, along with every last one of the Monster Souls in the Underground. At last, I was Asriel Dreemurr once more, and not only that, but I was the God of Hyper-Death. What's Hyper-Death? Truth be told, it was just something I came up with on the fly to sound all powerful and unbeatable, just to intimidate Frisk.

Frisk and I fought for control of the timeline, so that I could purge it from existence once and for all. Thankfully, by using her Hopes, Dreams, and sheer Determination to show me the same mercy she'd shown everyone else, and extend the hand of friendship, Frisk was able to save everyone, myself included. Free at last, I used my God-like power to break open the Barrier and free Monsterkind before I faded away once again.

Except, when I faded away… something…unexpected… happened.

…

?

Asriel's eyes flew open at the sound of a small explosion. Quickly sitting up and looking around, Asriel realized that he was in an unknown forest as a thousand thoughts ran through his mind.

Where am I? What's going on? How am I still alive? thought the boy in a panic.

"Relax, young Prince. I brought you here."

Asriel looked behind him to see a small white dog wearing some kind of device walking up behind him from a small crater. Asriel recognized the dog immediately. They called him "The Annoying Dog." Nobody really knew much of anything about him, but for some ridiculous reason, some monsters thought he was the creator of their world.

The dog began barking what sounded like a sentence, which the device attached to his collar translated. "I have fashioned you a new soul, one combining both a monster and a human soul, and sent you here, to this world, where you will be able to start anew, and get the Happily Ever After you rightfully deserve after all you've been through," the device said in a robotic voice.

"But, why?" asked Asriel, feeling a little foolish to be talking to a dog.

"Because you're the only one who can stop what's coming to destroy this world, such as Chara and Dr. Gaster, among other things," explained the Annoying Dog.

"No, no, no, Chara's dead. She died with me. Same with Dr. Gaster," said Asriel

"No, Asriel, Chara's alive. She lives on in Frisk's body. She may have failed to take control of you, but she's taken Frisk as her puppet. And now, they are destroying timeline after timeline, and they're heading this way. You're the only one strong enough to defeat them and save Frisk. However, that being said, your old body has degraded into dust, and in any case it would be unsuitable for this world. Behold, your new form," said the dog, before shaking himself off, sending small bits of crystal flying from his fur, which reformed almost instantly into a full-length mirror.

Asriel let out a gasp at the form that stared back at him. No longer was he a young goat child. Looking back at him was a tall and well-built human teenage boy of around 16 or 17 with pale skin, icy blue eyes, a mop of white hair wearing a green and yellow striped long-sleeved shirt, a locket on a necklace, black pants with a black leather belt, and black boots.

"I… I'm… human…" said Asriel as he began to feel his face and body.

"Yes, Asriel. You are now a 16-year old human boy who resides in Gravity Falls, Oregon. Don't worry, though Asriel, you may be human, but you still have all of the abilities you had as the God of Hyper-Death, save for Hyper-Goner. One timeline destroying entity is enough, wouldn't you say?" said The Annoying Dog, earning a small chuckle from Asriel. "Now, if I were you, I'd head up to the Mystery Shack. The Pines Twins are in town, and it'd be a good chance for you to meet some people and make some friends. If you'll excuse me, I must attend Gabe the Dog's funeral. I'm the keynote speaker, as he was a close personal friend of mine."

With a single loud bark, the Annoying Dog vanished into thin air. Asriel, seeing no other option, stood up and began to wander around the forest, hoping to find this… "Mystery Shack" place.

Asriel had hardly taken two steps when he bumped into someone.

…

Somewhere in the woods near a sleepy little town called Gravity Falls, Oregon, a boy of around 16 with a mop of brown hair and mocha brown eyes wearing a black jacket with an orange t-shirt underneath, blue jeans with a black leather belt, black and white sneakers, and a very battered looking blue-and-white trucker's hat with a blue pine tree on the front entered into a clearing, populated only by a tree stump as far as he could tell. This was the boy's favorite place to just get away from his crazy Grunkle Stan, who had been on a monster hunting trip with his twin brother, Ford, as well as his own crazy twin sister, Mabel, for a bit, and just relax, think, and write in his journal. This boy's name was Mason Pines, but he preferred to be called Dipper, mostly because of the birthmark on his forehead.

As Dipper sat on the tree stump, he pulled out a blue-and-white book that had the image of a pine tree and the number 3 on the front and a pen and opened the book to a blank page and began to write.

June 2nd, 2017

Finally back in good ol' Gravity Falls after the long, dull school year. I've been looking forward to this day since the end of last summer! Although, I gotta admit, ever since that first summer, with Weirdmaggedon and Bill Cipher, the summers I've spent here have been a lot less exciting.

Honestly, I kinda miss having someone to fight against. Like Gideon Gleeful, for instance. Believe it or not, he really has turned over a new leaf and has taken up being a magician. I just hope he sticks to card tricks and illusions and doesn't use REAL magic again. Oh, boy, that was a nightmare.

Mabel still hasn't given up hope of finally having her epic summer romance, even though she doesn't seem to realize that she's trying a bit too hard. Speaking of romance, Pacifica Northwest and I have these weird… moments. Honestly, it feels like my crush on Wendy Corduroy all over again. Speaking of Wendy, as I understand it, she's a lumberjack like her Dad and lives in Portland. Guess some things run in the family. Anyways, back to Pacifica. When we have these moments, it gets kinda hard to shake the feeling that she might be feeling the same way about me.

One way or another, I have a feeling that this summer might just be as interesting as the first one… here's hoping I'm right.

As Dipper continued writing, he began to hear something, like two people having a conversation. Dipper stopped writing for a moment, perked his head up and looked around, but saw no one, so he turned back to his journal. The voices continued to talk, which began to increasingly nag on Dipper, causing the teen to get irritated and slam his book shut.

"Mabel! That had better not be you and your friends! I'm trying to write in peace here!" said Dipper as he got up and made his way towards where it sounded like the voices were coming from. Before long, he walked directly into someone.

"Oof!" said both Dipper and the person he'd just walked into as they both fell to the ground. Pulling himself up, Dipper looked at the person, and saw that it was a boy around his age, although Dipper didn't recognize him.

"Sorry about that," said Dipper as he got up off the ground. "You know, I don't think I've seen you around before. Name's Mason Pines, call me Dipper," Dipper said as he held out his hand.

"Asriel Dreemurr," said Asriel, shaking Dipper's hand.

"So, you new in town?" asked Dipper.

"New to this world, actually."

Dipper frowned. "What d'ya mean?" he asked.

"Why don't we head back to your place? I'll explain on the way."

Well, this seems like a pretty good place to stop to me. Tune in next time as Asriel meets his one true love, Mabel Pines for the first time, as well as the rest of the zany Pines family. Until then, ta-ta!