Yeah I'm going that way with Spiderman, but there is more than just that. Also when the text is like this, it means peter is narrating.

Dipper, Mabel, and Pacifica take Peter to the mystery shack.

"What kind of place puts underwear over a stuffed gorilla?" Peter asked.

"Ask my Great Uncle Stan, he'll tell yah," said Dipper.

"You're Spiderman?" Pacifica asked.

"And is the stuff with said Girl Serrious because I really have a thing for super heroes," said Mabel.

"MABEL!" Dipler exclaimed.

"What its not like I have a chance with Captain America," said Mabel.

"He's currently seeing someone," said Peter, "anyway yes I'm Spiderman."

"Sorry sounding curious but how did you get your powers?" Dipper asked.

"The word is Currioussy," said Mabel.

"No it's not," said Dipper.

"Serriously," said Peter, "I already told the Avengers my victories twice that by the third time I skipped the part about my powers." (That's pretty much every Spiderman movie in the past 20 years in a nutshell.)

"We don't care about your victories, we just want to know how you got your powers," said Pacifica.

"Okay," said Peter, "But grab some snacks, this might take a while."

15 months ago:

My school was on a field trip to OsCorp, we got in because I'm friends with the founder's son, Harry Osborn. I was taking pictures of place with my phone because of how much I wanted to visit this place.

"Peter, stop goofing off and get back with the group," said Harry, "we're waiting because of you."

"Sorry Harry," I said.

I followed along with the rest of the group and then, because of my own stupidity I snuck off into the genetics lab where they were testing on different species.

I was admiring the work done when I felt a spider land on my hand. I actually kept my cool and stayed still...until.

"PETER!"

My friend Gwen Stacy made me flinch and then the spider bit me. Which then knocked me out

"Peter!"

Gwen came towards me.

"Peter are you alright?" Gwen asked.

Unbeknownst to Gwen that same spider then bit her. (That's right in combining both Peter Parker and Gwen Stacy's Spider origins together)

It wasn't until days later we found out about each other's powers. I decided to use mine as a superhero but Gwen wanted to keep hers a secret, because her dad, who is the head of the New York Police Department, hates superheroes.

Present time:

"And that pretty much sums up how I got my powers," said Peter.

"That how you became a superhero?" Mabel asked.

"Well it was mostly what my late uncle Ben said," said Peter, "with great power comes great responsibility."

"He was a wise man," said Dipper.

"And is this Gwen your girlfriend?" Mabel asked.

"Okay that's it no more teen magazines for you," said Dipper.

"Well actually its yes and no," said Peter, "We want to go out, but like I said, her dad really hates me."

"Okay that I respect," said Mabel.

"Well on the bright side Gravity Falls isn't the kind of Town in that much need of the Avengers," said Dipper.

"Really, what about Bill?" Mabel asked.

"I don't think they fight dream demons Mabel," said Pacifica.

"Well technically I'm not that much of an Avenger yet," said Peter, "more like an Avenger in Training."

"Eh, Close enough," said Dipper, "Relax, just because Gravity Falls is Weird doesn't mean we have a big league bad guy around here."

Meanwhile in a bunker in the woods.

A mysterious man is seen walking towards a freeze tube to see a certain being frozen in ice.

"There it is," said the man.

The man the throws down a sphere creating a small Electro-Magnetic Pulse shutting down everything in a 15 foot (or 4.572 meter for those in the metric system) radius, freeing the Dipper look alike turning into a bizarre creature.

"Who are you?" The Shapeshifter asked.

"Name's Osborn, Norman Osborn."

Ooh it just got real! Green Goblin meets a major villain from the Gravity Falls Universe. Wow this will be intense. Get ready for what's about to come, leave a vote, drop a comment, and share with your friends. See you next time.