A/N: Inspired by a comic by Markmak. Actually, pretty much the comic with a few of my own touches. Brilliant artist btw, go check it out on deviantart! Disclaimer: I don't own Gravity Falls.

Mabel narrowed her eyes as Dipper came home late (again) from his after school program. He was always late and it roused suspicions in her. She was technically the older twin and a protective feeling was roused on her at the sight of his dejected face.

Mabel straightened her sweater and fixed her crooked teeth in a heart warming smile. Her parents were insisting that she get braces before her twelfth birthday.

"Hey, bro-bro! Why the long face?"

Dipper shrugged and made a halfhearted attempt at a smile, "What long face?"

Mabel rubbed her chin thoughtfully as he ascended the stairs to their bedroom. "Hmmm. Looks like this a job for... Ducktective!" Mabel shouted, striking a pose.

She squealed excitedly and ran up the stairs. She'd finally be able to use the costume supplies she'd gotten for her eleventh birthday.

The next day, Mabel snuck out of her house and hid behind one of the houses Dipper passed on his way home. Mabel ended up drawing on the mud with a stick, there were several detailed mud swirls of unicorns and rainbows before the day was over.

Quick footsteps caused Mabel to jump up and peek around the edge of the white double garaged house. Mabel saw Dipper slow and then look up at the clouds for a minute. A contented smile crossed his face, Mabel didn't see anything wrong until two boys peeked at Dipper from around the corner.

A red haired boy grinned at his fellow before sneaking up behind her brother. Mabel's brow furrowed.

The boy snatched the green hat off with a ferocious yank. Dipper jumped and his hands flew up to catch the hat, but it was too late.

Dipper turned and knelt quickly to grab the hat from where it had fallen onto the concrete. A sneaker smashed the hat flat and Dipper withdrew his hand quickly.

"Not so fast, Nerd!"

Dipper shot the two bullies a harsh frown. "Please take your foot off of my hat."

"Look at your dumb face, nerd!" The red haired bully said, pointing at Dipper's now visible birthmark. The second blond bully echoed, "Dumb face! Dumb face!"

Mabel could see hurt blossom on her brothers face as the red haired bully finally took his foot off of the hat. Dipper snatched it back and sped off with ringing shouts of 'Dumb face! Dumb face! Dumb face!' to accompany him all the way to the end of the block.

Mabel meanwhile got redder and redder- her eyes burning with fury. She had just made up her mind to go and tell them off when a little voice seemed to whisper in her head a new plan... One that would get the bullies off her brother'a back forever.

As Mabel sped away she realized that it was a plan worthy of a Slytherin and totally out of character. Perfect.

#######One Day Later#######

Dipper trudged down the concrete, his cap pulled low over his face. The ginger and blond boy sneaked behind, nasty grins on their faces.

Suddenly and unexpectedly Dipper turned and gripped the hand that was raised to pull off his hat.

"Say 'Dumb Face' one more time! I dare you!" Snarled Dipper, both bullies too shocked to hear the slightly feminine lilt to his speech or the slight blush on his cheeks that signaled that Dipper wasn't quite right.

"Leave me freaking alone or I will make your life a living nightmare! Have I made myself clear?!" Dipper threatened his voice going deadly quiet at the end of his speech.

The bullies scrambled off as fast as their legs could carry them. Dipper smiled and pulled off his hat to free long brunette hair. Dipper was in fact, Mabel.

Little did the bullies know, that Dipper was sick that day... What they didn't know wouldn't hurt them, anyway.

Several weeks later, Mabel walked with Dipper across the school playground. Dipper's former bullies whimpered at the sight of him and steered alarmingly clear of him.

"Huh. They seem scared of me now. What happened?"

Mabel only shrugged,

"I dunno."