Pacifica Northwest

Pacifica Elise Northwest is a spoiled brat and the most popular girl in Gravity Falls, Oregon. 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, though this seems to be lessening as the series goes on.

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 talented singer and dancer. However, the crowd chooses Mabel, likely due to 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 desperately made 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 had won instead of Waddles.

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

In "The Golf War", Pacifica played against Mabel in a miniature golf-off. In the end, Pacifica and Mabel had to fight off the Little-Puttians and then went inside Grunkle Stan's car to her house.

In "Northwest Mansion Noir", she hires Dipper to stop a ghost, but the ghost was later on able to turn everyone into wood (including Mabel and Dipper). Ignoring her father (and her family)'s cheating ways, she decided to open the gate so all of the rest of the citizens could enjoy the party and the ghost could be busted.

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 had looked 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, though she can do little to resist that, until "Northwest Mansion Noir", when she ignores her father to do the right thing. After seeing all the horrible acts her ancestors have committed, she was greatly appalled, showing that she does indeed have morals.

Physical Appearance
Pacifica has long blonde 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 Taffyta and Vanellope have in Wreck-It Ralph. In both cases, the ruder ones were reforming to be more on the good side.