Underfalls: The COMPLETE Trilogy To A Gravity Falls/ Undertale Crossover

❤️Chapter 1: New Beginnings❤️

MabelPOV

I woke up to find myself in... Sans' room? I looked around, and sure enough, this was the funnybones' messy and disorganized room. It was a Saturday morning, and my first week of my new classes were over. But what confused me was the fact that I was in Sans' room. Not on the couch downstairs. But in an actual bed, with the skeleton himself asleep beside me. I held back my fear of waking him up as I stared at him, watching the back of his body rise and fall. It hitched as he began to stir, stretching and turning over to face me. My face flushed red in embarrassment as I realized I was staring, but he didn't seem like he was annoyed by it.

"Good morning Mabel," he yawned as he stretched his limbs, and wrapped his arm around me, and pulled me closer to his body. "Did you sleep well?"

"H-how did I get here? Last time I remember I was falling asleep on the couch and-"

"I feel bad now that you're living with us and you'd still be sleeping on that lumpy-old couch so.... You don't mind, do you?" I shook my head, giving Sans a hug. "How are so warm? You're a skeleton! You're nothing but bones!"

Sans let go of me, and pulled up the shirt under his hoodie to show me his ribcage, a neon blue stomach bulging out from it. I was shocked. "H-how is that even possible?!"

"Magic," Sans grinned  as he let his shirt fall, bopping his teeth to my forehead. He gave a stretch, before climbing out of bed, and I soon repeated his actions. "You wanna head to Grillbz for breakfast?" Sans yawned as he threw me my bag, and I digged through it to find a sweater with a burger on it, and a matching blue headband. I was about to pull off my pajamas, when I remembered that Sans was just across the room, watching me. I dashed around the bed and started to push him out. "Hey this is my room!"

I giggled as I shut him out, changing my clothes. The summer flew by fast, and I couldn't believe that it had gone by this quickly. I thought I was going back home with my parents in California, seperated by by my twin brother, Dipper. He was going to stay here in Gravity Falls, with our Great Uncle Ford, and leave me behind. But, a few weeks ago, me and Dipper had fallen down My. Ebbot, and encountered the many monsters of the Underground. That, including of Sans, a friendly little skeleton who loves puns, sleeping, and eating. We had met him deep in the cold woods of Snowdin Forest. He and his younger brother, Papyrus, guided us all the way to Snowdin Town, with puzzles and traps to lure us to the village. But, in a turn of events, Dipper killed Papyrus, and I stayed back to comfort Sans. And as I spent more time with him, I realized that Inwas falling in love. But that was no suprise. It seemed I fell in love with every guy I met, and they ended up dumping me. But it seemed... Like Sans was different.

When the skeleton was at the point where he couldn't take it anymore, he went to Judgement Hall, a passage right before the king's throne, to kill my brother. But I stopped him. He seemed like he weakened when I stepped out. And, as a final act, he sent us back home, making us believe that we would never see him again, and all that we had to focus on was Bill. But we were wrong.

Only a few hours after we had awoken back up home, Dipper had gone to fight Bill, while I broke the Barrier. Without a human soul. And I went to find Sans. And Toriel. And King Asgore. And every other monster that survived Dipper's grip. And I took them to the surface, to take Bill's soul. My plan? It was to bring everyone that my brother killed back, and make things right between humans and monsters. And with Bill's soul, we succeed. Sans almost died, but we did it.

Now, instead of going back home to California after the summer was over, I'm now staying with Sans and Papyrus in Snowdin Town, and not a single monster hates me. And now, I can stay in Gravity Falls and be happy with everyone. But there's still a lot I need to teach Sans. I wanted to introduce him to all my friends on the surface, and I hope he and his brother are okay with me bringing Waddles with me... And maybe I can show Papyrus the Mystery Shack! I'm sure he'd love it!

I reopened the door to find Sans asleep against the door, but his eyesockets flew open at the sudden movements. He stumbled to his feet, giving me his signature sleepy-skeleton grin. "Took you long enough," he grumbled as lead the way downstairs. Halfway down, I was pushed, and we fell to the living room carpet. "Oww.."

"OH. SORRY HUMAN! I DID NOT SEE YOU THERE."

I got up and hugged my new roommate, the first real I've ever gotten from him. He gave me a pat on the head as he dusted off his "Battle Body," dashing to the fridge to give me a container of frozen spaghetti. "HERE IS YOUR LUNCH, HUMAN! HAVE A GOOD DAY AT SCHOOL-"

"It's Saturday! I don't have school!"

"THEN WHAT WILL YOU DO?!?"

"I wanted to introduce you and Sans to all of my friends on the surface!"

"B-BUT..." Papyrus looked down, twiddling his gloved thumbs, " WILL THEY LIKE ME? THE LAST HUMAN WANTED TO KILL ME..." I shook my head as I took a skeleton's hand in each of mine, and zoomed out the door. "You'll love the surface I swear!"

•••

"And this is the Mystery Shack! Home of the weirdest things of Gravity Falls!" I lead my friends into the door, but instead of finding Grunkle Stan greeting a bunch of tourists, it was Soos.

"Soos?" The handiman turned around and grinned at me, blinking in suprise as his gaze fixed on the Skelebros behind me. "Hey Mabel! Have you come to show the town to your new friends?" I nodded, as I looked at Soos in confusion. "Yeah but... Where's Grunkle Stan and Great Uncle Ford?"

"You uh... You didn't hear? Mr. Pines and his brother left."

Author's note: So Gravity Falls is over huh? Dang I was crying so much, the feels were so intense. Also, thanks so much fir supporting me all this way. I wouldn't have expected even writing a sequel, so thanks for making this possible!