Once upon a time, it was a warm summer's night in Gravity Falls. Dipper and Mabel Pines were bored out of their minds.
"Hey Dipper", Mabel called out, hanging upside down on the couch.
"What?", Dipper responded absentmindedly, preoccupied by TV.
"Let's go frolicking in the woods!"
"Are you CRAZY?!", he cried, whirling around. "It's 10:48 at NIGHT!"
"But... The fireflies are out", she persisted.
"Ugh, Mabel, those woods are teeming with EVIL."
"Optimist beats Pessimist!" She yelped as she grabbed Dipper's arm and dragged him outside.
Dipper griped and whined... Until he saw just how nice it was outside.
"Wow," Dipper breathed. "It is nice out here."
"TOLD you!", Mabel gloated. "Now... Whoever catches the most fireflies WINS!"
Dipper laughed. "You're on!" They both ran off, shouting out to each other each time they caught a firefly. Dipper had finally loosened up, but as they chased fireflies, they unknowingly ventured further into the forest.
There WAS evil in those woods, and it wasn't far off from the Pines'.