"Dipper, my feet hurt!"

Dipper Pines had been listening to his sister Mabel complaining for the entire 2-hour walk through the forest. He rolled his eyes.

"We're almost there, Mabel. Just keep going."

"Well, what was so important that you had to show me that we had to walk all the-" She stopped and looked up. "Whoa…"

"Told you so." Dipper gave a satisfied glance to his twin, who was staring in awe.

"What…is that?" She said slowly.

The white-blue portal crackled with energy just above the tops of the trees.

"It's some sort of portal," Dipper said, flipping through the pages of his "3" book. "I haven't figured out which kind…"

"Fire, Dipstick!" Mabel started picking up pinecones. "It's a good thing I wore my pinecone-collecting sweater. We must commence throwing projectiles at the magical portal!"

"Mabel, stop!" He grabbed her arm. "It's just a portal. It probably doesn't even work."

"It's our job to find out!" She continued hurling pinecones at the electric circle. "Everything works in Gravity Falls! Mystery is everywhere! Mystery, and really bad-smelling Porta-Potties!"

"Whatever, just stop throwing-" Dipper's phone buzzed deep in his pocket. "Mabel, Stan just texted. We have to get back to the shack before dinner so he can rip off more poor tourists."

"Okay!" Mabel waved. "Goodbye, Mr. Mysterious-Portal-Thing!"

"Mabel!"

Dipper walked out of the clearing, not waiting for her to follow. Only after he'd gotten a few feet, he heard Mabel's voice.

"Wait…Dipper?" She said. "What is the portal doing…?"

He sighed and turned around to find the blue portal crackling with purple.

"Holy…"

"Get down!"

Dipper had no time to question his sister's command. He ducked behind a fallen tree just as the portal started shooting out bolts of violet lightning.

"Was it doing this before?" Mabel yelled.

"Of course not!" He responded. "Wouldn't I tell you if it did?!"

A scream came from the portal. Dipper looked up, trying to find the human source of the noise, but nobody else was around. After a few seconds, a slivery stream of water poured out of it.

"What is that?" He said, peeking out from behind the log.

"We need a front row seat, Broseph!" Mabel yanked his arm and pulled him out from their hiding place.

Dipper cautiously approached the metallic puddle, and then jumped back with a start while the liquid took a human shape.

Slowly, the liquid transformed from human shaped to an actual human- a girl a little older than Dipper with medium-length light brown hair, wearing a backwards hat, overalls, a white T-shirt, and sneakers.

"What the- who are you?" Dipper started, but the girl was lost in her own thoughts.

"Where am I?" She muttered to herself.

"You're in Gravity Falls!" Mabel announced cheerfully. "The home of the Mystery Shack, where you can see amazing, mysterious, almost-real artifacts from-"

"W-who are you?" The girl said, cutting Mabel off. She held out her hand, pointing with her index finger. "I-I'll use this, I swear!"

"Easy, Snapback." Mabel said, raising her hands. "We come in peace. Well, actually we were here already, so we're wondering-" Mabel leaned in. "What planet are you from?"

"Mabel, this isn't any weirder than anything that ever happened here." Dipper rolled his eyes. "But seriously, who are you?"

Just like before, the girl didn't respond. Instead, she pointed to the portal. Yellow lightning surged from her fingers.

"What did you just do?" The twins cowered behind the log once again.

She turned and pointed at the log. But instead of it being zapped with electricity, the log was lifted in the air for a few seconds. The girl winced and it fell back to its original spot.

"My head!" She groaned. "Either way, you guys need to tell me where I am. Annie and Ray are going to be so freaked out. Not to mention, my parents will report it, and the plant…you guys better start talking."

"No, you need to start talking." Dipper demanded. "How did you get here? Why can you do all this stuff? Who's Annie? Who's Ray? What is the plant? Who are you?"

"And where did you get those overalls?" Mabel kneeled down and asked, "Because I'm thinking of making a new sweater design with them on it!"

"Is she…always like this?" The girl raised her eyebrows.

"Unfortunately, yes." Dipper rolled his eyes. "But the real question remains: who are you?"

"Alex." She looked at them with her wide brown eyes. "My name is Alex Mack."