Pacifica Northwest

Pacifica Northwest is the most popular girl in Gravity Falls, and is a spoiled brat. She is the great-great-granddaughter of the supposed founder of Gravity Falls, Nathaniel Northwest, and because of that, she acts like she's the boss of everyone. However, he is later revealed to be a fraud. Her arch enemy is mainly Mabel but her other enemies are Dipper and Grunkle Stan.

History
Pacifica first appears in "Double Dipper", when she competes with Mabel for the title of Party Queen at the Mystery Shack party. She and Mabel sing and dance, showing that Pacifica is a very good singer and dancer. However, the crowd chooses Mabel, probably because of her spirit and friendly disposition. But then Pacifica bribed Old Man McGucket and she threatens people with an ice cold stare to get her way to the top. She then leaves with a large part of the crowd to go to the after-party on her parents' boat.

In "Irrational Treasure", she makes a speech for Pioneer Day, and then insults Mabel for her silliness. She taunts Grunkle Stan when he's put in the stockade. She is later informed by Dipper that her great-great-grandfather, supposedly the founder of Gravity Falls, was a huge fraud. This causes her great worry, as it would discredit her entire family.

During "The Time Traveler's Pig", Pacifica appears and makes a very unkind remark about Mabel. Later, when Mabel and Dipper are traveling through time, the two go to an alternate timeline where Pacifica is the winner of Mabel's prized pig, Waddles; this horrifies Mabel, who convinces Dipper to go back in time and reverse the incident. At the end of the episode, Pacifica is seen being attacked by a chicken who she won instead of Waddles.

She makes an extremely short cameo in "The Deep End" although only her hair can be seen.

Personality
Stuck-up, sarcastic, rude, arrogant, snotty, and mean, Pacifica is a stereotypical popular blonde girl, having money, style, and talent. She is the show's diva and looks down cruelly on "weirdos" such as Mabel and her friends Candy and Grenda, and lords her ancestry over the people of  Gravity Falls. Her parents spoil her and seem to encourage her cruel behavior.

Appearance
Pacifica has long blond hair (which is most likely dyed or a wig since both her parents have dark hair) and at the dance wears a purple jacket with a short lavender dress, along with a purple belt. She also wears black leggings with cream boots. She wears heavy purple eyeshadow and lavender hoop earrings.

During Pioneer Day, she wears a light turquoise colored dress with a purple belt wrapped around it, and a gold to yellow belt buckle in the front. Black leggings are underneath with her cream boots, she also wears a brown hat with a raccoon tail attached to it. Hanging on either side are untied strings with purple arrowhead shapes on the ends, and she has a skinny purple bracelet around her arm.

Trivia

 * Her name is a pun on the U.S. region "Pacific Northwest," a region containing Oregon, the state in which the show is based and where creator Alex Hirsch spent his summers.
 * Pacifica and Mabel's rivalry is very similar to the one that Vanellope and Taffyta have in Wreck-It Ralph.