Pacifica Northwest is the most popular girl in Gravity Falls and a spoiled brat. She is the great-great-granddaughter of the supposed founder of Gravity Falls, Nathaniel Northwest, and because of this, she acts like she's the boss of everyone. However, Nathaniel is later revealed to be a fraud. She is the opposite of Mabel, causing Mabel to be her arch nemesis, and vice versa. 
Pacifica is first seen 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 bribes Old Man McGucket with money and threatens people with an ice cold stare to get her just above Mabel Pines and win the party crown. She then leaves with a large part of the crowd to go to her after-party on her parents' boat, and the crowd carries her away on their shoulders.
In "Irrational Treasure," she makes a speech for Pioneer Day, and then insults Mabel for her silliness of wearing a sweater of a dog playing basketball. She also 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. Dipper also gives her the secret cover-up document as proof. This causes her great worry, as it would discredit her entire family.
During "The Time Traveler's Pig," Pacifica appears at the Mystery Fair and makes a very unkind remark about Mabel. Later, when Mabel and Dipper are traveling through time, the two accidentally create 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 she won, instead of Waddles.
She makes another cameo in "Boyz Crazy," entering the Gravity Falls Civic Center and Buffet with her friends to watch the Sev'ral Timez concert. She is seen buying tickets, and later watching the concert, holding up a sign that says "Sev'ral Timez."In "Gideon Rises," she is shown through one of Gideon's surveillance cameras, throwing darts at a picture of Mabel.
In "Mabel's Guide to Colors," Pacifica surprisingly takes part in Mabel's survey of Gravity Falls' favorite colors. Pacifica answers with barely a hint of mockery.
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. She seems to think that her family is better than everybody else's, and that they are perfect. She has bullied Mabel and also picked on Stan once during Pioneer Day, seeming to take the opportunity to tease someone related to Mabel.
Pacifica has long blond hair and usually wears a purple jacket with a short lavender dress, along with a periwinkle belt. She also wears black leggings with cream colored boots. She wears heavy purple eyeshadow and lavender hoop earrings.
During Pioneer Day, she wore a light turquoise dress with a purple belt wrapped around it, and a yellow belt buckle in the front. She also wears black leggings underneath her cream boots and has a coonskin cap. Attached to her ears are purple arrowhead earrings and she has a skinny purple bracelet around her arm. She is still wearing the heavy purple eyeshadow.
- 107. "Double Dipper"
- 108. "Irrational Treasure"
- 109. "The Time Traveler's Pig"
- 115. "The Deep End" (no lines)
- 117. "Boyz Crazy" (no lines)
- 120. "Gideon Rises" (no lines)
- 10. "Mabel's Guide to Colors"
"Aw, 'it' thinks it's gonna win. Wait, did you hear that? People cheering for the weird girls? Yeah, me neither."
"May the better partier win."
"Oh look, Mabel here found her REAL twin!"
"Wow, I'm embarrassed for you. Give her a hand, everybody!"
- Her name is a pun on the "Pacific Northwest" region of America, a region containing Oregon, the state in which the show is based and where creator Alex Hirsch spent his summers.
- Pacifica's favorite color is hot pink.
- She has become a relatively popular character, which Alex Hirsch didn't expect because she is such a terror compared to Mabel. According to Alex Hirsch, she will also have some development in season 2.
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