Prior to the gremlin incident, Ruby Deagle showed up at the bank where Billy worked and claimed that Barney broke her imported Bavarian plastic snowman the same morning. Billy tried to apologize and offered her money, but Deagle threatened Billy and claimed that if she saw Barney, she'd give him a slow and painful death. She considered putting him in her spin dryer. Barney then jumped on her and broke the rest of the plastic snowman's head. She then threatened Billy and the dog and told them, "I'll get you... when you, at least, expect it!"
Later, Barney was with Billy and his parents to see Gizmo come out of the box. When Barney sees Gizmo for the first time, he licks his paw, head, and ear and Gizmo says, "Woof-woof? woof-woof". Barney also shared sleeping in the same bed with Gizmo and Billy that night. Later, Barney also watched Gizmo spawn the first batch of Gremlins when getting wet by Pete Fountaine, although Barney was slightly jealous of Gizmo, he cared dearly about Gizmo and Gizmo liked Barney from the start, and they both soon got along with each other, Barney and Gizmo both disliked the new Mogawai.
Gizmo was then playing music with a trumpet for Barney. Afterwards, Stripe and the other evil mogwai tied him up in Christmas lights. Billy freed him, thinking it Mrs. Deagle that did it. Billy's father, Randall Peltzer, decided to take Barney with him to Billy's grandmother, then took Barney after he was done with the science invention convention. Barney was not seen again until the end of the film when he raced into the store where Stripe and Billy were fighting to eliminate each other. As Barney raced, he met Gizmo driving a pink Barbie car twice with Gizmo saying "Woof-woof" twice while racing to find Stripe. After Stripe was killed, Barney saw this and went back to Billy's house. When Mr. Wing took back Gizmo, Gizmo said "Bye-bye, woof-woof!"
His current where-abouts are currently unknown, as he was not mentioned in the sequel but he probably remained at home in Kingston Falls until his eventual death.
- He was portrayed by a dog known as Mushroom (who Steven Spielberg stated in the original film's commentary was one of the best actors in the film).
- Barney was oringnally going to get killed and eaten by the gremlins but that scene was cut for being too dark.
- During the making of the film, Barney, (Mushroom), bit the animatronic Gizmo, this delayed filming for about 7 to 9 hours.