Waddles' first appearance is with Mabel in the opening credits, in which Mabel is hugging him.
His official series debut is in "The Time Traveler's Pig", where Mabel wins him in a "Guess the Critter's Weight" game who is, of course, run by a carny. She looks at the animals, until one pig oinks, which she interprets as him saying either "Mabel" or "Doorbell". Taking this as a sign, Mabel asks the host of the game to let her guess the pig's weight. He tells her its name, "15-Poundie", giving her the answer to its weight. She takes the pig, renames it Waddles, and quickly forms a great friendship with it.
The bond between Mabel and Waddles is strengthened each time the twins travel through time, resulting in her spiraling into depression when she loses him to Pacifica Northwest in the only successful Dipper timeline. After realizing how much Waddles means to her, Dipper goes back in time and sacrifices his chance with Wendy to allow Mabel to re-win Waddles. To show her appreciation, Mabel sends Waddles to retrieve the caramel apple Robbie is sharing with his new girlfriend, Wendy. This startles Robbie, causing him to drop the apple and knock over a barrel of hot water, painfully shrinking his pants.
In "Fight Fighters"Waddles sits next to Mabel as she plays a card game with Grunkle Stan and before the fight asks if they want her to send Waddles on Robbie again, referring to "The Time Traveler's Pig". He is also there when Mabel watches Grunkle Stan while he watches TV. At another point he sits next to Mabel at the table while Dipper worriedly paces about his upcoming fight with Robbie.
Grunkle Stan later uses Waddles in attempting to scare off two kids. At the end of the episode, Waddles eats the bag of candy Stan received while everyone else watches a horror movie for the remainder of the night.
Grenda, Candy and Mabel are later seen taking pictures of Waddles and adding captions, similar to internet memes such as the "lolcat".
In "Boss Mabel", Waddles is first seen watching Cash Wheel with Dipper, Mabel and Grunkle Stan while eating Chipackerz. When Mabel becomes the boss of the Mystery Shack, she makes Waddles her secretary. Near the end of the episode, Mabel asks Waddles for his opinion on Stan's apology song.
Waddles is a light pink pig with a light brown/tan dot on his left eye, with light brown/tan spots on his back on the left side. His snout is light pink, he has a black curly tail, his hooves are brown/black and he has a rather plump face. Waddles also weighs 15 pounds, and his favorite food is Caramel Apples. On Summerween, Waddles wears a costume which looks like a business suit, a black coat, a dark brown collar, a white shirt and red tie, and black shoes.
- Waddles was named by Aury Wallington, who is one of the writers for the show. She named him after her own pet pigs she owned during her childhood. 
- Alex Hirsch gave Mabel a pig because his sister, Ariel, always wanted one.
- Intro: "Gravity Falls Main Title Theme"
- 109. "The Time Traveler's Pig"
- 110. "Fight Fighters"
- 112. "Summerween"
- 113. "Boss Mabel"
- 114. "Bottomless Pit!"
- 115. "The Deep End"
- 116. "Carpet Diem"
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