Multiverse Part 2: Demigods In Gravity Falls

Chapter 1: Dipper's Dilemma

Dipper Pines was no stranger to weird things. He himself had a weird birthmark and a weird sister, after all. He had seen a man with six fingers, a triangular shaped demon, gnomes, a portal to other worlds, a bunker under a tree, and many, many other things. But a random person appearing on his bed? That was a new one. Dipper had been heading up to his room to just relax when he saw a stranger sleeping on his bed. Before freaking out and waking the guy up, Dipper studied the teenager. He looked around 16, with black hair and an orange shirt that read "Camp Half-Blood". He also had on a necklace with a few beads on it, with the beads having pictures on them, and one had a bunch of names along with... was that the Empire State Building? Dipper decided to wake the guy up, so he shook his shoulder and said "Hey." The kid muttered "Just a few more minutes, Mom." Dipper shook the guy's shoulder and loudly said "Wake up!" The teenager jolted and woke with a start, saying "Yow! Talk about a wake-up call, jeez!" Then he looked at Dipper and asked "Who are you?" "Dipper Pines. Also, you're in my bed." said Dipper. "What?" the teenager asked, then he looked down and said "Oh. Sorry." He jumped off of the bed and held out his hand, saying "I'm Percy. Percy Jackson." Dipper shook his hand and asked "How did you get in my bed?" Percy looked around and then looked back at Dipper, then said "This'll sound weird, but you have to trust me. I have no idea." 

After a long discussion with only a few answers, Dipper took Percy to see Grunkle Ford. They found Grunkle Ford in the basement, pondering over the dimensional rift. "Grunkle Ford!" Dipper called. Grunkle Ford turned around and saw Dipper and smiled, saying "Dipper!" Then, he noticed Percy and asked "Who's this?" Percy held out his hand and said "I'm Percy Jackson." After Grunkle Ford shook Percy's hand and Dipper explained the situation, Ford said "Well, Percy, I'm sorry to say this, but I'm not sure I can help you right now. I've got another big problem I have to deal with." "What is it?" Percy asked. Ford showed him the rift and told him about how dangerous it was. Percy rolled his eyes and said "Oh, boy, a Doomsday warning. Haven't had enough of those in my life." Ford looked like he was about to inquire, but Percy held up his hand and said "Before you ask, don't. Let's just say that where I come from, the Greek myths are real, along with prophecies." Dipper decided not to ask questions, and Percy said "Hey, if I help you out, you could help me out, right?" Ford laughed a little and said "Well, if you could, then we'd gladly help you. But I don't see how you can help, no offense." Percy smirked and replied "Got any water?" 

Percy, Ford and Dipper all headed to the nearest body of water, and Percy said "Stand back." Ford and Dipper obliged, and Percy concentrated. Then, he raised his arms, and the water began to rise, higher and higher. Percy made a fist and rose it, and a fist of water rose up out of the lake. Then, Percy opened his hand and relaxed. Ford and Dipper were shocked. "Incredible! How did you do that?" Ford asked, shocked. Percy turned and said "I'm the son of the sea god Poseidon, it's a trait his children have." Ford nodded and Percy said "So, still not convinced I can help?" Ford shook his head and replied "OK, it's a deal. If you can help us deal with our problem, we'll help you get back home."